"Yes I do have an IR, but no I have not really used it, and frankly find the idea of using it is daunting since the training for the IR was a entirely on pre-planned school routes"
Speaks volumes about JAA IR training, doesn't it. I guess you are
very familiar with the approaches at Bournemouth, Oxford, Cranfield, or Cambridge?
Best to do some flying with an IR pilot, doing some airways routes. You have an IR so you can be PIC. Pick some nice destinations in Europe and he'll be more than happy to come along just for the trip
Legally, it's not illegal to execute a DIY instrument approach, in a G-reg. (There are some complications doing this in an N-reg, due to a FAR regulation whose number I don't recall off hand)
How to do one satisfactorily depends on your attitude to risk. I'd use GPS
plus VOR/DME fix and descend to 500ft over the highest obstacle within 5nm. Having got QNH from a nearby proper airport and verified it against the GPS derived altitude. This rule often yields an "MDH" of 1000ft or so. I've gone below that but wouldn't do it again.
As regards a position fix, well use your common sense. If you get it wrong, you will
die, so it's desirable to get it right. (Actually personally spoke to one man who did a CFIT at an estimated 120kt but the angle was quite shallow and he is still here, having spent some time in hospital).
So,
two independent position fixing methods, and obviously one of them should be a GPS or radar.
If you have no nav gear, a PAR approach is the #1 choice.
Next option: you can get a radar letdown from most military (LARS) units. They do it over nearby surveyed terrain and they will take you down to 1000ft over the obstacles. You just hope to be in VMC by then.
Next option is to get VDF from some airfield (most can do this) out over the sea and descend out there. I guess D&D on 121.50 can also give you a fix over the sea; I don't know if they like doing that. Obviously if you have enough fuel then a PAR approach is better because ending up over the sea under an OVC003 limits your options to coastal airfields with offshore wind
But surely you knew all this
Anybody who flies in IMC without nav equipment, and particularly a decent GPS, needs their head examined, IMHO.