the London reds wouldn't show up his friends/(i.e. friends of Franco/working in London)
Francisco F. Franco (1892-1675), Spanish general and dictator who, with the help of Germany and Italy, was victorious in the Spanish Civil War.
During the time of the Spanish Civil War, Moscow considered the collective security of the Allied nations to be more important than any other issue. They wanted Britain, France, the US and the Soviets to stand firm against the Nazi-Facist threat. To that end, it was official policy not to upset the Western democracies by sponsoring worldwide revolution. Thus, at the time of the people's revolution against Franco and the Falangists in Spain, there were several Red or Communist groups. Some joined the fight against Franco, but because of the Moscow line, some were actually fighting on the side of Franco. The two groups were represented among the Marxists in London and the US. Some English units left for Spain to join the battle, as did the Abraham Lincoln Battalion from the United States. But some, following the Moscow line meticulously, would not expose those agents of Franco working in London.
--George Orwell, Homage to Catalonia, Boston, Beacon Press,1962.