Removal of tenant with no contract

Hello all,

I have a tenant who has lived in my flat for a number of years but I would now like him to leave. I gave him about 3 months written notice but he is refusing to leave until he finds a suitable new place to live (He wants to buy, not rent).

The tenant was a friend so stupidly I never asked him to sign a AST agreement. He has said that because no AST exists, he doesn't need to leave. I believe I can take court proceedings to evict him but do I have any lest drastic options?

Is the fact that no AST exists a benefit to me or the tenant?

Thanks
Andy.