I doubt it - usually manufacturer warranties last only a couple of years and even then generally require the unit to be returned to them.
Dunno what's wrong, it could be the light source that is failing, in a TV that old it's probably a CCFL not LED's and they can and do fail over time.
Replacing a CCFL is often cheap and easy - but you're still going to be faced with the labour charges and the cost of the replacement part, if it wasn;t standard but custom made for this range then it may well not be available anymore.
Might be worth looking around for a local repair service that does a fixed-fee fault find and repair estimate then you can decide whether to get a new TV or not.
If you get a new one you're getting some years worth of warranty with that and it'll probably be a better one anyway. You could certainly get a much bigger screen for £600 now...and a bunch of other stuff like Smart TV and so on.
As said, John Lewis
include a five year warranty with their price