Hi Rob
Been pondering / researching this again (keeps my mind off what I should be doing..) and I think you're right, you're going to have to swap the telly!
As no new 12 volt receivers have RF output anymore, the only way forward with one of those is an RF modulator which you said you can't be a**ed with, You have no AV inputs so no point going there....
The 12v Sky boxes are OK but you are limited to what you can use them for, although if you have a home subscription your card
may work (although this is obviously contrary to the terms of the Sky contract, but you wont get "premium" channels; fimls & sport)
The good news is that there are loads of places selling off analogue flat panels quite cheaply at the moment, all of which will have scart connectors, so a Maplins type set up will work fine; (also your power usage on 12v should be lower on a flat panel) or go for a monitor with AV inputs and run that off the box
Not much help I know, but if you do get a new tv you can go back to looking for a s/h suitcase receiver kit on the bay of eees for around £30, so with a new telly it'll probably be cheaper than just buying a new Maplins kit at £100 that you can't use - how's that for logic
Andi