LL is entitled to compensation above the value of fair wear and tear. This is an important distinction and it does not mean that he can claim new for old. Lets do an example:
You have left a stain on one of the carpets. The carpet was 5 years old. The landlord tells you that a new carpet for the room will cost £200.
In this example, you may be asked for the full £200 and shown an invoice, however you are not responsible for the full cost. A carpet in a rental property might be expected to last 10 years at most, so the landlord has only actually 'lost' 5 years of 'value' or half. Therefore you would be liable for half of the total cost, ie. £100. In some circumstances, if you have a long enough tenancy, nothing is effectively claimable from the deposit as everything is covered by fair wear and tear. It is important to note that a landlord is responsible for the upkeep of his property; whereas landlords will try to make you believe that anything that isnt identical to when you moved in is your responsibility. This applies to everything - drawers, lampshades, beds etc. Don't ever agree to pay the full replacement cost of an item.
Which scheme is your deposit protected with? I suggest you familiarise yourselves with their rules now as there are often time limits to adhere to.
The landlord should contact you (within 10 days of the end of the tenancy ending is the guideline) and suggest how much they wish to deduct with reasons. At this point, raise your concerns if you have any and state what you are prepared to offer. If you can not agree, then you should refer the matter to the deposit scheme. They will take evidence from both sides and make an independent decision on how much you owe. This is free for you, so don't be worried about asking for adjudication if you feel your landlord is being unreasonable. It is worth noting that the deposit money is yours in law, and so the burden proof is on the landlord to prove that you have caused damage. If he can not do this then he can not claim any amount from the deposit.
A deposit is just a convenience for sorting out damage. If you have caused damage that is greater in value than your deposit then you are still liable to pay for this but the landlord will need to proceed through the small claims court in order to enforce this. The small claims court is an informal setting where legal fees are capped at about £200, so its not as bad as many people expect it to be.