Hughen,
When buying on finance, car supermarkets and car main dealers alwaysc seem to come up with extra charges as you get to sign the finance agrrement.
I used to buy a new car every 18 months and every time was asked to pay fees for documents. I could understand say a £30 fee but £250 is a rip-off.
In this current economic climate, why don't you go back to the salesman and say"Sorry, I can't pay any more money on top of the interest as this is what I have budgeted for" They will try to offer spreading the payments a little or maybe promise you a deal of the century and drop the fee to £200 but stick to your guns and say "No. I'll have to leave it" and head for the door.
I have got away with this on the last 4 new cars I purchased so there is nothing to lose by trying, just be assertive when talking to the salesman.
Please post again and let us know how you get on.