Scotty D

So, i have fixed it, problem was a broken wire after all, one of the wires inside the black rubber gaitor/sleeve that goes between the body to the boot lid. It had been repaired in the past and was the thicker brown wire. I didn’t see this on first inspection as the repair was good being done with solder so I thought the chances of it having broken again were slim - a wrong assumption on my part. Having gently pulled at the wire, I was delighted when it came out one end broken as I knew then that it was mystery solved and an easy fix. All lights working together with boot lid release button which is working from key fob too. 
Thanks for the input and happy motoring. 

An old post I appreciate but wonder if you solved this, I have same thing happening. Read somewhere else that taking a live feed from battery to reg plate bulb will solve but not tried yet. Apparently doing this with the live wire “reminds” the ECU that it should be sending power to the boot lid. Sounds odd but worth a go I’d think.

 Thanks