Matt
As FW says, an ab initio student will probably need somewhere between 60 and 70 hours before being up to the standard required to pass the exams. I'd budget for 65 hours (£16k inc VAT at those rates, plus overheads - course materials, exam fees, medical, etc.), but remember there are lots of students that have taken more than 70 hours (sometimes a LOT more!) to get their ticket. Don't run out of cash with only a few hours left to do!
Two things:
If you have a limited time in which to complete your training, don't assume that you'll get in 2 flying hours per day, 7 days a week; I think that's very optimistic. Apart from things like the good old British Wx, I think you'll find the average over the course will be more like 1 hour per day - if you're lucky.
Also, don't be tempted to pay for the whole course up front in return for a bigger discount unless you are satisfied the school is financially sound. I'd suggest negotiating something around blocks of, say, 10 hours at a time. There are lots of schools struggling at the moment and you'll be right at the bottom of the food chain when a receiver prioritises the list of creditors.
TTB