Len Deighton generally declines to make any strong political statements.
I've found a few references to his political views from various interviews available online, and he invariably declines to make any real commitments, preferring to remain fairly neutral and nonpolitical.
From the Independent, January 2006 (bold emphasis mine):
If there is a common factor, it is his sympathy with what you might call the poor bloody infantry. Even now, he will not concede that he has any agenda against the generals, the leaders, the politicians, even after his most recent book, Blood, Tears and Folly, a damning overview of the major campaigns of the Second World War.
What he does say is that people in positions of power, who may be sending people off to be killed, should expect to have their deeds examined in rather more detail than those being sent to be killed. It is tempting to see it as a straight class issue. But he deflects the question.
"I was born in a workhouse," he says. (He was, in Marylebone in London, in 1929, though it was just up the road from the hospital, and his parents were by no means destitute; at that time, his father was a chauffeur and skilled mechanic, "in service" to the family of a senior keeper at the British Museum. His mother was a cook. They all, in fact, lived in a mews near Baker Street.) "It trumps the ace of everybody else, doesn't it? Where do you go that's lower than that? So I feel free to criticise anyone I choose. I just speak as I find. I'm not a member of any political party. I hesitate before I join hands, as the old saying goes. What I say is based on my own experience."
From the Telegraph, 2009:
He thinks Britain is even less meritocratic and democratic now than in the Sixties. “But I’m not a militant. I’m not trying to overturn the system, I’m just trying to be a part of it.” He cannot be accused, as John le Carré often is, of being nostalgic for the Cold War. “I think the world is a better place now.”
From the Deighton Dossier, March 2012 (bold emphasis mine):
The narrative [of The Ipcress File] seems to twist 'social' norms: the hero is working class, rough around the edges, yet is more cultured, eats better food and better read than his bosses. Did the character's approach reflect perhaps your own worldview at the time in London, when attitudes were changing?
LD: Well, there were already plenty of class warriors around at the time I started writing. John Osborne, Alan Sillitoe and Arnold Wesker, who wrote Chips With Everything, were ‘angry young men’. I was of about the same age, but I wasn’t angry.
What did I have to be angry about? I had had spent six wonderful years studying art. [...]
When I graduated from the Royal College of Art my diploma came from the hand of the Duke of Edinburgh. In the speech he made to us wide-eyed little van Goghs he said that artists were lucky. Artists, he said, could wend their way through all sections of society and all classes too. I took him at his word and despite being born in the Marylebone Workhouse I have found that a clean shirt and sober tie – plus a sense of humour – overcomes many social limitations.
I am not a class warrior. I respect and admire skills and education. Britain’s public schools have a long tradition of teaching the Victorian virtues; a belief in God, loyalty, modesty, justice, prudence, patriotism and sacrifice: I value those characteristics. When I poke fun at authority it’s not a matter of class, it is because authority is too often given to lazy and incompetent cronies. Prejudice of any sort is evil; it is illogical and destructive. ‘Give every boy an equal opportunity,’ I say. Never mind whether he comes from Eton or some workhouse in Marylebone. Girls too, of course!
He does, however, call himself a capitalist. From the Deighton Dossier, November 2012 (emphasis mine):
Yes, [Major Erich Stinnes] was based upon a grim-faced East German pen-pusher who had lived in Moscow where he became a 'Germany specialist'; at least, that's what I was told. He turned up rather too often among the people I knew in Berlin. I don’t think he was assigned to watching me (he would have been more friendly had that been the case), but he was a dedicated Marxist while I was a self-confessed capitalist. We didn't become friends!