Moving out early

Hello,

I need some advice please. I am currently renting a property on a 11 month contract, although i am actually on my 2nd contract. Due to a change in my work I need to move out and also I can no longer afford the place where I am currently. I have always paid my rent on time and I am sad to have to leave where I am. I have given my 1 months written notice but now the landlord says I have to pay all the rent till the end of my contract-another 4 months. I cannot afford to do this as I have a new apartment to pay for and anyway it does not say anything like this in my contract that if I go early I need to pay to the end. I am worried about this. Please can anyone tell me if the landlord can do this and what would happen if i don't pay? thank you.