bookworm, thanks for pointing that out!!
Basically, if you are not going to fly IFR and stay below 4,500' over a large swath of the UK then it is very likely that you will not need 8.33 until the blanket installation required Europe wide by the end of 2017.
I had a chat with some of the purveyors of avionics at Sywell on Friday and one chap reckoned that a good Narco 810 should fetch around £500 on the second hand market which will be a useful offset to the £1,000 - £1,500 + fitting for a new radio. I suppose as the final countdown ticks away the non 8.33 units will be worth less.