I had the good fortune of meeting both Ken MacLeod and Iain Banks in Cambridge last year. Ken is, or at least used to be (haven't checked recently), a relatively frequent contributor to the alt.politics.socialism.trotsky newsgroup. His political background is Mandelite Trotskyism - he was a member of the British Mandelite organisation at some point in the past, and these days seems to be friendly with the broad Trotskyist re-evaluation / regroupment thinking centered in e.g. the journal What's Next? MacLeod is pretty open about his SF being a vehicle to explore different political philosophies.
Iain described Ken as being more leftwing than himself, so I guess that puts him somewhere a bit to the left of Labour (his non-SF books contain numerous quips at the expense of the Guardian, called the Grauniad as I recall).
Peter -- Peter van Heusden <pvh at egenetics.com> NOTE: I do not speak for my employer, Electric Genetics "Criticism has torn up the imaginary flowers from the chain not so that man shall wear the unadorned, bleak chain but so that he will shake off the chain and pluck the living flower." - Karl Marx, 1844 k*256^2+2083 OpenPGP: 1024D/0517502B : DE5B 6EAA 28AC 57F7 58EF 9295 6A26 6A92 0517 502B