Well many thanks chaps, however.......
It's not the IOD fuse cos I took that out many moons ago.
It's not rebooting the system cos that happens every morning when I reconnect the Battery.
It's not Fuses Nos 5 and 20, cos they're now both out, and its not better.
It's not (as someone else said to me) a dicky battery, as I changed that, and it's exactly the same.
What I have discovered is :- that to lock it (noting the key fob now doesn't do anything) you have to sit in it with all doors closed and Ignition on. Then Lock it by pushing the switch on the door panel down, and it all locks. Turn ignition off, use the inside door handle to unlock the drivers door, and then get out. then lock the drivers door manually outside, and it's all then locked. A right pain......
Anyway, all the time it's running it's useable, even though this latest scene of events is somewhat annoying. I did read the riot act to it a couple of years ago after when I replaced the Thermostat and Radiator, with the threat that it would be going to meet the great recycler in the sky if it went wrong again, and in fairness it has behaved itself until very recently.
I'm just optimistic that there's something silly that has failed, and that I can easily/cheaply sort it out, otherwise I can see my patience wearing thin if it continues to mess about.