well the sellar of the tv should not have made that call, he should have arranged for panasonic to look at the tv, as they will mine, their opinion is the only one that matters..
now maybe panasonic would have said there is nothing wrong with the tv, maybe not, but they need to see it, and give their opinion, and then you can take it from there..
im not sure where you go from here gel, you probably should have went through this with us lot on here first, before accepting the stores terms, but its done now, i think you should contact the store, explain that you're not happy with losing £250, and ask them for the money, if they refuse then politely inform them that you are going to take legal advice, and they will hear from you soon, then let em sweat for a few days, see what happens..