Thank you. Ignore the fact that he may be a vulnerable tenants. He is clearly worldly wise when it comes to money! To your disadvantage I might add.
Assuming that the tenant has a Assured Short Tenancy, you need to issue a Section 8 notice under the provisions of the Housing Act 1985
and here is some more reading
Your application would be made on ground 8 that there are 2 months of arrears at the date of the hearing (he can defeat that by reducing the arrears below two months on the day in court), ground 10, that there are other arrears, 11, that he has regularly failed to pay rent, and anything else listed in the box at the top.
Provided 4 months of the tenancy agreement have already passed, you might want to also give him a section 21 notice to quit at the end of the term. http://www.landlordzone.co.uk/pdf/servingS21.pdf
Can I clarify anything else for you?
I am happy to answer any specific points arising from this.
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