damage to property - non-return of deposit

I have served my tenant's with their S21a (to be out by 31st July 2011).

I have agreed to go around to the property next week to go through and identify all areas of the property that will either need making good / repairing or replacing before they move out. With the plan that this will give them 7 weeks to do the work!

I have already spotted damage to the pvc front door, a significant stain on the front room carpet, damage to the wood and paintwork around the property and oil stains on the driveway.

I did take some photo's before they moved in, but I'm not sure if I covered the carpets and driveway.

What is considered to be fair wear and tear?

If they are not prepared to put the house back to it's original state how do I show them a bill to justify keeping the whole of the deposit (it won't cover the cost of replacing the carpet let alone anything else).

Am I entitled to contact the utilities to see if there is any outstanding money owed?

What happens if they don't leave a forwarding address?

Many thanks.

Debbie