Kenny - Personally, I'd argue that they should not have incurred any costs above the quoted figure without getting your approval first.
Therefore all costs above £2,500 are there problem and not yours.
A quick google search came up with this:
http://www.adviceguide.org.uk/wales/...ge_repairs.htm
Perhaps do a bit more searching on line and print off some legal stuff before you go back to them.
Given they have not done 100% of the work, offer them a % of the £2,500 quoted for the whole job and remove your car from them ASAP.
Good luck, Paul.
