I accept that these may not be the most land-to-energy efficient of energy sources ... and it's something I know very little about ... so I was wondering if anyone more enlightened could wise me up.

I'm under the impression that presently we're paying all kinds of subsidies to a considerable number of farmers to either grow nothing or over-produce oil-seed rape and other surplus crops ... I could well be wrong, but this is the impression I get, maybe this is no longer the case ... maybe it never was?

Could biofuel crops not be grown on exisiting farmland which is, in one or other of the above stated manners effectively not efficiently productive? I have no idea if there's enough farmland in such a situation to make any kind of practical contribution to potential biofuel demands or whether these crops yield enough of a viable return to a farmer ... or even whether such crops cause any environmental damage themselves.

Is this a totally stupid and ignorant idea? If so why? I honestly know very little about all this but would be interested to learn more.