As you may have seen you can do a small claims online and it can be all sorted in a matter of weeks.
This reads a bit better and can be improved upon. They don't need to know all of your correspondence, just a summary of why you are going to the SCC. Keep it simple.
"I agreed to buy a car from Jon Hunt for £2400 and paid a deposit of £400 [Insert date]. The advert described the car as being mint condition. On Friday September 10th before I was due to pick up the car the seller contacted me and said: 'when you come, I would recommend bringing a jerry can to fill with fuel just incase. The car doesnt like running sometimes with 1/4 of a tank'. Upon further probing Jon claimed ‘.....the pump wont keep up with the carbs. Its not designed for that'. This problem was not mentioned at time of sale and the car was described as an ‘everyday runner’ and ‘mint condition’ in the advert.
In light of this new information I backed out of the sale and requested my deposit back as it was not mentioned at time of sale even though I asked about such issues. I specifically asked Jon if there were any problems with the car and we discussed the only two problems he claimed the car had (rev counter and fuel gauge).
I have asked for my deposit back as a result of this new information as I no longer wish to purchase the car under those circumstances and the seller has refused to reimburse me the deposit“
Thats absolutely brilliant! Thanks for that.