In the 1930s, Communists across Europe rose to the challenge of fascism: 'the open terrorist dictatorship of the most reactionary, most chauvinistic and most imperialist elements of finance capital', as Comintern secretary Georgi Dimitrov defined it.

The leading role of Britain's Communist Party in the fight against fascism was only made possible by its expanding base in the working class, both in workplaces and in local communities. So strong had the Party become in small towns and villages such as the Vale of Leven, Chopwell, Maerdy and Nelson in Lancashire that each had earned the nickname 'Little Moscow'. Leiston in Suffolk became the countryside equivalent.

The British Union of Fascists had emerged in 1933 under the leadership of former Labour Party junior minister Sir Oswald Mosley. Among its most enthusiastic backers was Lord Rothermere, proprietor of the Daily Mail. The real character of Mosley's thugs was shown at his 1934 rally in Olympia, when black-shirted storm troopers savagely beat anti-fascist protestors. Later that year, a BUF rally in Hyde Park was “drowned in a sea of working class activity” by a counter-demonstration of 150,000 people.

Mosley's most humiliating defeat came on Sunday October 4, 1936. His attempt to stage an anti-Jewish march through east London was crushed in the 'Battle of Cable Street' by a huge throng of workers mobilised by the Communist Party and the Young Communist League, supported by the ILP and other socialists and progressives.
  The Metropolitan Police batoned the crowd in desperate efforts to clear the way for the BUF in their paramilitary uniforms. But 300,000 anti-fascists blocked the road, overturning trams and raising barricades. Many of the arrested demonstrators received harsh treatment at the hands of the police and several were sent to prison with hard labour.

One particularly important factor in the Party's ability to mobilise large numbers of people in London, Birmingham and elsewhere was its growing work among tenants. In particular, women such as Jessie Eden and Ella Donovan played a prominent part alongside Bob Graves and 'Tubby' Rosen in ferocious battles against 'decontrolled' tenancies, rack-renting, unsanitary conditions, evictions and the other features of slum landlordism. Stepney Communist councillor (and future MP) Phil Piratin explained how this campaigning undermined the fascists in his classic book, Our Flag Stays Red.

The right wing of the labour movement advocated ignoring the fascists and abstaining from anti-fascist activity. The Communist response—that retreat before fascist aggression merely increased its appetite—proved correct time and again throughout the decade.

In mid-1935, the 7th world congress of the Communist International had elaborated its call for a united working class front of Communists and social democrats at the core of a broad people's front, to rebuff the fascist tide. That fascism led directly to war had already been shown in 1931, when Japan attacked China, and in 1935 when Italy invaded Abyssinia (Ethiopia).

In 1936, German and Italian military forces intervened to assist General Franco's revolt against the democratically elected socialist and republican government of Spain. This struggle became the focal point of a worldwide campaign against fascism. Millions of people in Britain rallied in solidarity with the Spanish Republic, while Tory and right-wing Labour leaders adopted the shameful policy of 'non-intervention'.

For Britain's Communists, the Spanish cause spawned tenacity and sacrifice on the scale of the General Strike. By the end of December 1936, the Young Communist League had filled the first of 29 food ships. Communist women's leader Isabel Brown was one of many outstanding campaigners, stirring the hearts of open-air crowds with her appeals on behalf of Medical Aid for Spain.

The spirit of Spain also helped produce the biggest vote so far, at the 1936 Labour Party conference, for Communist affiliation. More than one-quarter of the votes were cast in favour, including those of the miners, engineers, train drivers and furniture makers.

This, in turn, inspired a Unity Campaign from January 1937, launched after talks between the Communist Party, the Socialist League (in which Labour MPs Stafford Cripps and Aneurin Bevan were prominent) and the Independent Labour Party (headed by Fenner Brockway and James Maxton). Large and enthusiastic meetings took place throughout Britain. The campaign drew in the Left Book Club, established in 1936 and soon boasting a network of 1,500 local discussion groups. Its growth reflected the renewed interest in the international situation and in Marxist ideas.

In promoting a 'Popular Front' of anti-fascist forces in Britain, Harry Pollitt pointed out that—unlike in France—it would be overwhelmingly working class in composition:

'Here the decisive majority of the population are industrial workers, the most class conscious are already organised industrially and politically. Our first job is to bring about unity within our Labour Movement'.

It is a self-serving myth peddled by ultra-left anti-Communists that the CP in Britain, or in France for that matter, abandoned principled positions in order to chase after middle class allies for the People's Front.

But Communists were keen to demonstrate that socialist and Communist ideas stood in the progressive traditions of their own country. AL Morton broke new ground with A People's History of England and the Communist Party history group was founded to counter bourgeois approaches and analyses to history. Led by Communists, the Unity Theatre movement and the Workers' Music Association expressed the class struggle in cultural forms. Eminent scientists such as JD Bernal and JBS Haldane applied Marxism in their specialist fields, popularising science amongst working people in the process.

Thousands of people flocked to Communist-initiated pageants in London, Glasgow, Manchester, Liverpool and—sponsored by the South Wales Miners Federation and the LRD—across south Wales which celebrated working class and progressive history, linking it to the 'Popular Front' and the struggle in Spain. A theatrical spectacle with 3,000 performers, commissioned by the Cooperative movement and devised by Communists composer Alan Bush, film-maker Montagu Slater and director Andre van Gyseghem, filled Wembley Stadium with 78,000 spectators.

But by far the most heroic aspect of the Spanish crusade was the formation of International Brigades to go and fight fascism. Felicia Brown had been the first Communist from Britain to join a militia in defence of the Spanish Republic. She died on the Aragon front in August 1936.

London clothing workers Nat Cohen and Sam Masters set up the Tom Mann Centuria. Beginning with only a dozen British volunteers, it grew rapidly with the direct assistance of Harry Pollitt. In October, Spanish prime minister Caballero agreed that the Communist International could raise International Brigades to come and defend democracy. An international recruiting centre was set up in Paris and a training base at Albacete in Spain.

Around 2,200 volunteers went from England, Scotland and Wales to fight Franco and the fascists. There can be no exact figure because the Tory government threatened to use the 1875 Foreign Enlistment Act against 'illegal' volunteers. Keeping records and lists of names was difficult and dangerous. However, since weekend trips to Paris didn't require a passport, there was a way around the authorities for those whose ultimate destination was Spain. In France, active support from Communists, workers and peasants opened the paths over the Pyrenees.

Volunteers for the British Battalion came from all walks of life, although the great majority were from industrialised areas. They were accustomed to the discipline of work in the factories and pits. From their unions they had learnt the value of organisation, democracy and solidarity. The commissar for English-speaking volunteers in the battalion, Communist Peter Kerrigan, set out the standards expected of volunteers:

'All recruits must understand they are expected to serve. Tell them: this is a war and many will be killed. This should be put brutally, with a close examination of their hatred of fascism'.

Many volunteers already knew how to exercise leadership and take action in working class organisations. They understood the importance of setting an example and leading from the front when necessary. They were united in their aims and prepared to fight for them. The International Brigades provided a shock force while the republican government recruited and trained its own armed forces. The Spanish people knew they were not fighting alone.

In Britain, Communists accounted for about half of the Brigade volunteers and the 533 of them killed in action. Prominent Party members who served in Spain included Bert Ramelson, Christopher Caudwell, Len Crome, Lou Kenton, Bill Alexander, David Marshall, Ralph Fox and John Cornford. Among the many women in medical units were Communists Thora Silverthorne, Sylvia Townsend Warner and Mary Valentine Ackland. Soon after her return, Silverthorne became the founding General Secretary of Britain's first independent trade union for nurses.

In September 1938, Juan Negrin, head of the Republican government, announced that the International Brigades would be unilaterally withdrawn from Spain for diplomatic reasons. However, General Franco failed to reciprocate and German and Italian forces remained, continuing their brutal suppression of those standing by the legitimate, elected government of Spain.

Before leaving for home, Sam Wild, commander of the British Battalion, declared: 'The British Battalion is prepared to carry on the work begun here to see to it that our 500 comrades who sleep for ever beneath Spanish soil shall serve as an example to the entire British people in the struggle against fascism'.

In October, the International Brigades began to depart, the words of Dolores Ibarruri ('La Pasionaria') ringing in their ears: 'You can go proudly. You are history. You are legend'. The Republican government fell to Franco the following year, although Spain's Communists fought to the bitter end.

As fascist aggression was advancing in China, Austria and Spain, Britain's Communists and their allies worked strenuously to build a 'people's front' powerful enough to force the Chamberlain Tory government to adopt a policy of collective security in defence of peace.

But the ruling class traitors would not budge from their determination to appease Hitler, hoping that Nazi Germany would turn its fire eastwards towards the Soviet Union—and away from the British Empire. The Daily Worker and Claud Cockburn's journal The Week exposed the nest of Nazi sympathisers—leading financiers, industrialists, government ministers, military chiefs and newspaper editors—who plotted at the Cliveden mansion of Lord and Lady Astor.

The Party's 15th congress took place in September 1938, as Prime Minister Chamberlain was scuttling back and forth to settle the fate of Czechoslovakia with Hitler. Palme Dutt and Communist MP Willie Gallacher warned the congress that Chamberlain was preparing to betray Czechoslovakia and therefore to betray peace, rather than form an anti-fascist alliance with the Soviet Union. Their assessment was proved right when less than a fortnight later Chamberlain returned with the Munich Agreement.

That same congress also acknowledged that the Communist Party had under-estimated the democratic and progressive content of the national question in Scotland and Wales. This rectification opened the way to full support for the establishment of Welsh and Scottish parliaments.

Britain's labour movement leaders refused to rouse the people into mass action against fascist aggression. Cripps and Bevan were expelled from the Labour Party for joining the Popular Front campaign. Communists continued to be ejected from leading elected positions in the Amalgamated Engineering Union and others, while the TUC General Council voted to prevent Arthur Horner taking a seat on behalf of the Miners Federation of Great Britain.

Undaunted, Communist policy and leadership continued to attract many people who feared that appeasement was making war inevitable. By 1939, Daily Worker circulation had grown to more than 40,000, with a weekend average of nearly 80,000. Communist Party membership reached 15,750 by late 1938 and 17,750 by July 1939.

The Young Communist League was also winning young workers through a series of strikes for the Apprentices Charter. It demanded higher pay, day-release training and trade union representation. Clydeside, Tyneside and Manchester were major centres of militancy.

The show trials of former Soviet and Comintern leaders such as Kamenev, Zinoviev and Bukharin did little to check the growing popularity of the Communist Party and Marxist ideas in Britain.

For much of the 1930s, the Soviet Union had appeared a bastion of peace and stability amid a world of mass unemployment, fascist aggression and colonial exploitation. Communists everywhere helped publicise its enormous economic, scientific, social and cultural achievements.

At the same time, the hostility of the imperialist powers towards the Soviet Union was well known in working class and progressive circles. Within the labour movement, the followers of Trotsky—who had been expelled from Russia—were regarded by many who came across them as anti-Communist, anti-Soviet oppositionists, disrupters and defeatists.

When respected lawyers, politicians and diplomats from the US, Britain and elsewhere attended the Moscow show trials and confirmed that the defendants had indeed confessed to being members of a 'Trotsky-fascist' campaign of espionage and subversion, Britain's Communists were not alone in believing that such plots had indeed existed.

Reports of mass-scale repression, labour camps and executions in the Soviet Union could all too easily be dismissed as another round of capitalist propaganda against socialism.

There is no serious evidence that the British CP leadership knew of the full extent of the purges, or of the degree to which the incarceration of several million Soviet citizens—many of them loyal Communists—lacked any justification.

When they learnt about the arrest and disappearance of British Communist Rose Cohen—who had gone to live in Russia with a Comintern official—Pollitt, Dutt and Gallacher angrily demanded to know the truth from the authorities. But they did not make their protestations public.