i rented through foxtons a while back and did enquire at the time as to what would happen should i suddenly need to move out. the negiotiator i delt with at the time informed me all i would need to do would be to pay the admin fee for the name change to the contract if someone else was found to take my place within the flat. i cant imagine they're allowed to take that 11% fee as well, esp if they now have someone else in there in your place, paying the rent you were paying previously...