I agree with Alex - the margins at flight schools are much tighter than most people would think so discounts are rare.
However, you may be able to negotiate on small up-front payments (some places give a discount for only £1000 at a time up front payments because it eases administration) which leave you less at risk, or you may be able to negotiate slightly on price if you try to fly in quiet periods or on a standby principle. You would need to be aware of the down sides of this approach however!
Before you start your course make sure you know the true course cost - does it cost the "package price" or are there extras - fuel surcharges, exam fees, landing fees etc. In this way hopefully you will be able to make a more informed decision on how much a course costs.