ast with prvious landlord

Rent Arrears

I broght a house at a auction in Dec with 2 tenants on a ast fom sept 09. The ast is still in the old landlords name and wondered how this effects me with following problems;

Tenents have only paid me 2 out of six weeks owed, can I do the section 8 or 21b in my name?

Do they have more rights or less if the ast was with me. Or is it just the same?

Is the ast valid?

Should I give them a new ast, if so how do I get missed rent?

They are very elusive and claim to be on sick leave since Nov and I have never met one of them. I spoke to local benifits office and they seemed to indicate benifits would not be paid but refered me back to the tenants for info on a recent letter sent to them.How can I tie them both down to sort problems?

I fellow landlord said he would just go and give them 7 days to leave and arrive on 7th day to change locks. It sounds highly illegal to me?

As they do not have ast can they be asked to leave any sooner?

Am I putting myself at risk by not giving them new ast in my name?

Many thanks for any help
A