Ok, let's get this straight.
You signed a contract in which you and your landlord agreed that you would pay £448 a month? Well, he can't change the contract on whim. For him to charge you more would be a breach of contract, which is illegal. To change the terms of a contract, both parties have to agree to it. You obviously don't, so that's that. He could try to evict you but he has no reason to do so unless you have destroyed the house or something.
This sounds fishy, are you sure you're not forgetting any info? It makes no sense for a landlord to do that, and if he has count yourself lucky! Get your deposit back and go somewhere else, this person sounds like a nightmare to do bussiness with...