I have managed to sort the problems with our TV!!!!
After extensive searching ont'Internet, I found a description of the fault and possible cure. It seems that Panasonic, Sony, Samsung and many others use the same power supply board and so the fault can surface on many brands.
It seems that some of the electrolytic capacitors used on the power supply boards are failing early. I opened up our set, taking care to let the power dissipate inside (overnight) and looked carefully at the electrolytic capacitors on the power supply board. Sure enough, 6 of them had "blown" - that is the top had
bulged and a tiny hole appeared where excess pressure will have bled off. They were all 3,300µF, 10v. A bit of looking around and I found some Panasonic branded high temperature ones at CPC Farnell at 96p (inc VAT) each. Add a bit for handling & postage and the bill came to £12.19. Did the exchange and reassembled the TV and VOILA!
Far cheaper than £350+ for a replacement TV.
Please note that you should only attempt this if:
a. You are prepared to brick your TV if it all goes wrong;
b. You have turned the power off and allowed the power supply to discharge;
c. You don't come chasing me for compensation if (a) occurs or you haven't allowed enough time at (b).
Happy fixing if you try it, other wise £180 minimum for a new power supply board apparently.
Colin