Allied Insurance have just quoted me £80 through Fortis Insurance, which I've just accepted and that includes walking on roofs, in fact anything up to a height of 15m, but not including the window I'm working, which I'm not fussed about. And it's not tools either, but I've got my ladders insured under a different policy. Thanks for the advice guys
Chris
EDIT: midlandsinsurance.co.uk have just got back to me with a quote of £82 and same as above, so worth checking them out too