rent arrears

Rent Arrears

Hi
I have a proper tenant problem.
He owes me 3 months rent.
I have send him a letter of intention giving him 14 days before I issue proceedings.
He has already told me that he is going to be difficult.
the 14 days will be due on the 16th of February.
1. I intent to issue Proceedings for rent arrears only and not
section 8 or 21.
2. The amount of rent is still accruing.
3. The AST is an RLA agreement dated from 15th April 2011 to 11 am
13th October 2011.
This tenant moved in on the 15th April 2011 but he said that he got paid on the 28th of every month and that it would be better for him to do so. I agreed and wrote on the addendum. RECEIVED THE AMOUNT OF £175 RENT FOR THE PERIOD 15TH TO THE 28TH OF APRIL INCLUSIVE.Which date do I use in order to calculate the rent owed in the Summons and can I say the rent is accruing since the tenant will be there?.
Thank you for the work you all are puting in I find it most helpful.