I also dealt with similar situation with two of my previous landlords. I contacted them by email and told that if they dont change my locks then i will deduct it from my next months payment.As Conniff said its not an good idea but a simple email like that worked for me. Unless you have a bad landlord then you will have to seek more expert advise. My personal view -Worst case scenario- get house insurance, keep payments u to date,stay on the good side of law and, look for a new flat and give notice and move out and avoid bad people. But before worst case scenario someone will be able to give more expert advise to sort the issue.