It don't matter what "warranty" he gives you, you have SIX MONTHS in law, under the sale and supply of goods and services act.
Very simply any major fault that occurs within 6 months is considered to have been there at the time of the sale, he cannot get around this, as it is the law of the land.
It's his responsibility entirely, he just sounds like a complete wanker, another arthu daley.
Ask him if he'd mind talking to trading standards as they can shut him down on the spot.
In a small claims court with you having evidence you wouldn't have a problem, most county court judges are very normal, ie in touch with reality unlike all the other judges, jp.
tabetha