It's a real mixed bag out there. I'm still restricted and one school I was at paid £20 an hour and I argued to get £10 on days when there was no flying, to cover petrol. The next one paid £25 an hour. The last one paid £18 an hour with a small daily retainer which covered petrol.
I think with the winter coming, if you're doing a good job and the school doesn't want to lose you, you've got to argue the case for being on a salary. Otherwise, with wet weather, short daylight hours etc. leading to less flying, you'll find yourself better off at Tescos !