Don't know what your problem is Blue, just nip up the road to Intelligent Energy PLC in Loughborough and buy yourself a fuel cell pack.
Only weights about 20 kilos, so remove the boot, clip on the pack, and you're off with 4 hours of running time on one filling (this is running time for their electric bike with a 6kW motor).
Only problems I can think of are, where do you tank up with hydrogen, and I should imagine a price in excess of £2k.