I think that you are still liable for the repairs mate.
Unfortunately, the I'm not paying them answer will get their backs up a bit.
You're better to take a nicely nicely approach. Write them a letter explaining that you do want to bring the matter to a satisfactory conclusion, but that you don't agree with the assessment of the damage. You accept that there is some payment due, but that you would like them to allow you to seek a second opinion on the cost of the repairs.
Any reasonable person would give you this opportunity.
You might also be able to agree a reduced amount with them if you can pay it in full. Typically I've beenable to negotiate with a debt recovery agent to 75% of the outstanding sum in your case this would be �600.
You phone them up with the same kind of attitude saying your desperate to get this settled etc, and would be in a position to pay it in full, today (via switch) if you could just agree a figure suitable to both of you. Start low saying that you've managed to get �500 together and would they be willing to accept this as payment in full?
They will say no thats not enough (thats a guarantee). Now you keep calm and tell them that you might be able to offer some more, but you'll need to go away and see if you can sort something out with the bank. You'll call back in half an hour.
Phone them back in 20 mins, make sure you speak to the very same person. If they're not available, call back. This is important as you already have a raport with this person and they are aware of how desperate you are to settle the account.
No tell them how difficult it was to get this together, i.e. you had to borrow money from you mother / father / brother / priest to get another �100 together. You canoffer them �600 tops.
this has wiorked for me on at least two occassions.