Changing Monthly payments to weekly

Tenancy Types and Management

Hi
One of my tenants lost job and could not pay for about 3 months.He was paying £375 pcm. His payments are still in arears but he has now found a job and has started paying weekly. I have AST agreement dated 8 June 2007 and have not renewed it since so it is now periodic tenancy.

1. I want to obtain a new AST agreement for six months with Weekly payments of £86.50 instead of monthly. I want to say 2 weeks payment in advance (like we say 2 months payment in advance)in the agreement. He is paying now £100 weekly, so this excess £13.50 I want to use to repay my arrears.

2. Can I obtain an AST agreement for less than 6 months. If yes, can I use the standard RLA agreement or I have to amend it in anyway.

3. In fact I am selling this property and do not want to evict him, if possible. Also a periodic tenancy can not be assigned to the new landlord, so I want to obtain new AST agreement for 6 months which can be assigned on sale. New buyer is also keen to keep the existing tenants.

I shall be greateful your valued advice.

Hari