Informal Forum Guidelines - Terminating tenancy

I am currently renting a flat (in a flat share), and having lived there from Sept 07 to April 08 (6 months), I would like to move out. I have given my landlord a 1-month notice, and he has replied by asking me to pay for the remaining rent of four months. The tenancy agreement is assured shorthold tenancy and the term is 12 months. The agreement contains no break clause, and although it says that I have to give notice, it does not state how much in advance the notice has to be given. I am pretty sure that my deposit isn't protected, as he has never made any mention of it. The other person living in the flat is the landlord's daughter, who is joint owner of the flat and she is the reason for my wanting to move out, and I doubt that the tenancy is being formally declared (not sure what the correct term is). What is the best way of dealing with this situation? I am not looking for any trouble or trying to get out of paying rent. any advice welcome!

If you have a 12 month contract without a break clause you are legally obliged to fulfill the terms and conditions of the tenancy until the end - however - if you were able to find or the landlord find a substitute tenant to take on a new lease then from the day the new tenant starts your tenancy should cease totally and you have no liability for the new tenant. Any costs to find the replacement tenant may have to be paid by you and ensure that you and the landord sign a surrender document to formally terminate the lease if mutually agreeable earlier than the contract end date.