AST term?

General Discussion

We have had a lovely family in our house for 3 years, they moved in when the house was brand new, they wanted a 12 month AST in December 2012 so it is due for renewal 3rd December 2013, we have today (27th July) received a letter saying they want to move out on 2nd September 2013 so are terminating the contract. How do we stand on this. We need to relet the house immediately but there is lots of work to do i.e. new carpets, decorating. Should we ask them to pay the rent till December or until we can re-let the house. How do we stand legally. We feel there must be a good reason for them to want to move out so quickly but are worried about our mortgage repayments.