Legal Letter Needed

I need a letter to be written to a builder who did some work for me approximately five years ago. He was supposed to oversee work done to my property and employ and coordinate the necessary manpower for a job for which he verbally quoted £5000.

As the work started this man became very erratic with his visits to my property and his contractors were warning me that they would have to leave the work unfinished if he didn't pay them - I had already given the builder £1500 at this point, a fact which he does not dispute. I then had to pay his contractors directly in order to get the work finished.

I had a letter approximately a year or two ago asking me for the balance but i ignored it, I have now had another letter threatening court action if I dont pay £2500 within 14 days.

The man does have legal knowledge so I need a very strongly worded letter with the necessary legal terminology to sort this matter out.