Bob,
Sure, Johnny L's do give a good service and extended warranty - but, you can usually get the same at a better price elsewhere.
You can then buy your extended warranty from the likes of Domestic and General, at a well below the difference between web and Johnny L's prices.
Couple of years ago, I bought a LCD from Comet. They wanted about 300 quid to add 4 years additional warranty. I bought extra warranty over the phone from Dom & Gen, whilst still in Comet, for about 80 quid.