Thanks for the tip Pondboy, I filled it to the inner brim (on the side stand as I have no centre stand). Light came on after 217 miles, and when I got to fill it at 221.5 miles, it took 12.25 litres back to the inner brim. That works out at a little over 82 to the gallon, but I expect that should improve when the engine loosens up, it's only got 1300 miles on it so far.
( I do wear rather a slippery jacket)