Phil
I agree 47p a litre is tempting. Had a quick look on Google and it seems the answer is - not yet. At the moment you can only convert single & multi point injection VAG engines, although some places are offering direct injection (FSI) conversions on other manufacturers. VW are trialling LPG conversions on direct injection engines. Google also threw up there seems to be some doubt over the long-term future of LPG ..... along with increased servicing costs, additional wear on engines valves etc.
For fuel economy & GTI performance, there's an all-new VAG 2.0 TDI diesel Bluetec - 204 bhp, 295 lb ft torque, 48 mpg est. Goes in the Audi Q3 in 2010, not sure if it's planned into the rest of the range any earlier (i.e. Mk6 Golf). I appreciate that involves buying a new car which does negates any fuel cost saving etc., and waiting 3 years!
Robin