Just an update if anyone's interested.
Having checked through the PSU (now I have the circuit), there was nothing wrong with any of the power components.
A simple S/C 1n4148 diode was preventing the main PSU starting up. That got the set powering up, but no backlights. That's a seperate section of the PSU. The cause of that not working was the PSU Ic had failed.
It took a while as the only place I could find the device was Farnell, and I wasn't going to pay £5 postage for a £1.38 part, so I had to wait until I had other things I needed to make up a sensible order.
Now it's all working fine.
I guess what happened is the PSU controller went faulty turning the power mosfet on permanently, and for once the fuse blew and not the transistor.
Now all I need is to find the Sky remote code for this set. Anyone know it? I've tried all the AOC codes listed by sky and they don't work. These sets also go under the brands of Envision and Norcent, but I've not seen any codes listed for those brands at all.