Thanks for the comments guys. I did leave it for about 30 mins, tried again and it was fine, so therefore I have some sort of intermittant issue. The only thing I did differently was use a lower amp hour battery but shouldn't make a difference I guess. I also read in the forum that the flashing lights means over temp protection activated - C5 was obviously cold....
Well I will keep trying it and let you know how I get on, but as we speak it's working, but still dirty.
Had a great time at Goodwood Revival - looked a pillock in the period garb though!
Cheers, Giles