If he saves up £400 in 6 months he will have a better telly than he can get now for £400 as they are just getting better and cheaper all the time. It's a better strategy to save for something where you can put away an amount of money you can afford rather than borrow money which you may not be able to afford to pay off.
I had a loan for a car once when I was younger and although I never missed a payment I would never do it again, the only thin I have borrowed money for since that is a mortgage and even then I made it as small as I could afford!