I hardly dare post this as I don't want to offend the gods who control my P38 but it seems that after two years of boring everyone with my running problem I may have the answer. I have found here in Spain a fabulous 'mobile mechanic' called Mark who is ex Army REME and knows Landrovers/Range Rovers inside out. Stuck on a sloping dirt track and unable to leave it at the garage guy in town Mark came out with all the kit to work in the field. Changed the gearbox oil and internal filter, engine oil and filter - replaced the thermostat and then cast an expert ear on the running. Misfire on the left side he said and most likely a spark plug. I had explained that for no apparent reason after starting and running cold ok it would lose power as soon as the engine gained any heat and run slow up hill, not changing down unless I pushed the Sport button and even then still trying to change up after a few seconds. He would have started on the spark plugs but knowing I could do that I pushed him on to the nasty jobs that I didn't like. So had the spark plugs out left hand side- all looked good - LPG seems to burn clean-and just for trial replaced the old plugs that were still around - went for test drive and on the hill coming back engine failed to a tickover. When finally back replaced the original plugs and noticed that the rubber part of the lead on the one at the back of the engine seemed to be very tight against that metal exhaust manifold that I'm told is a heat shield. Got out the hammer and bashed the shield down out of the way of the plug lead - went for test drive and lo and behold - actually drove like it should - accelerated and changed down as normal - almost perfect - after two years of limping around .... Anyway, Mark says because I use low ratio on the hill here (not really necessary) it causes wind up and wind up inhibits the automatic gear change. I used low range to get home up the hill sometimes because of the lack of power ! I also asked if the ECU had adjusted to my fault/problem and therefore was going to continue feeding wrong settings to fuel etc. He said disconnect the battery for 30 mins and this should reset the system. I know you will think I'm a plonker for not recognising a misfire but when it happened I just didn't know what was causing it and changed MAF, TPS etc etc. So I was bemoaning the fact of being in Spain and not being able to get hands on help from you forum people but now maybe I can stay here ! Oh, got a puncture coming back from the test drive ............so life is not perfect.....

Great feeling :)
I had a similar issue on my Jeep once - HT lead grounding isn't always easy to spot.
I don't think low ratio causes wind up on P38s because they have a viscous centre diff, vehicles with a locking centre diff do get wind up (like most defenders) so he's not totally wrong. I suspect you'll find your gear change works better once everything has re-adjusted to running on 8 cylinders. Drive it and let it relearn. Enjoy! :)

Kind of you to understand that it's not that easy to recognise where an intermittent fault comes from. I did think of starting it in the dark to see any spark flashes but never quite managed to stagger out to the car after the bottle of wine......
I said the same as you about diffs etc but Mark said in low range it has a 'limited slip mode' which causes lock up on a dry road. He said never use it (unless you are in a swamp) as it causes damage and bad lock up. This was the advice they gave all their drivers !

Yes it would be, because the Army used Defenders which will wind up the transmission whereas the viscous coupling on a P38 won't.

Ah - so much to learn - I have a long way to go ....

Does disconnecting the battery lose the stored running settings in the ECU ? Should I do that ?

On a P38 the only thing disconnecting the battery does is cause you to have to reset the windows and tune in the radio, it has no effect on the ECU. To do that you need to use your diagnostics to reset the adaptive settings.

Oh yes Gilbert - I sort of remember that now. Knowing what you have said before it makes sense to reset the adaptives because after so much bad running with misfiring on the one cylinder at least the system must be pretty screwed up. You don't know how good it feels to actually be able to put your foot down and the car to accelerate and show some desire to respond after so long. I understand that if I can remember how to use my Creader thingy and reset adaptives I should then run on petrol for it to set up again before allowing it to change to LPG ?

You can't reset adaptives with the CReader, you need to use the RSW software that you got to do that. Once reset, it might be a good idea to run on petrol for a bit to let it learn things.

Oh thanks - getting senile and muddled with these devices - forget what they can and can't do.....have to get the old laptop out !