It's done it twice over around 8 pushes of the button in the last week so needs looking at , never done it before although the lower tailgate plays up more, I've got a finger hole to open that when/if it plays up. The upper always releases until now. Luckily, I read somewhere that a slap on or near the reg plate can release it and it does. Everything looks good but I lubed the movey bits anyway(lower tailgate, carpet panel removed). The button and spring is spotless ,electrical connections the same. Obviously being intermittent it's a pita to trouble shoot. The slap is causing whatever is faulty at that point to start working again, any tips on what needs looking at lads?

Do you hear the motor operating (i.e. mechanical non-opening), or is it not always operating (i.e. electrical) ??

When you say connections are spotless, did you check the wire crimps inside the connector housings ? The copper wires can corrode inside the crimps. Could also be a broken wire inside the loom. Use a continuity meter & wriggle the wires.

FYI I had mechanical issues on my Green P38 for a while where the upper tailgate would not latch properly. Ended up replacing the latch mechanism. My issue was identical to this video

Thanks Pete. No motor noise at all when it plays up.
The lower tailgate does make a motor noise and fail to unlock occasionally but I've got a finger hole to operate it manually when that happens. The upper tailgate thing is new, never done it in the 4 yrs of my ownership.
I'll give the connectors a good looking at when I've a bit more time.

An update and another query...I checked the electrical connection again and gave it a good clean out with bits of mig wire and contact cleaner and it's not done it since so fingers crossed on that. However, the lower tailgate release is playing up more often now. I have an access finger hole to release it manually but had a look at the issue today.
When I first got the vehicle nearly 5 yrs ago the lower hatch was occasionally not unlocking but I thought it was sticky latches because they were pretty gungy and a good clean of them seemed to sort the issue in the main but still occasionally failed hence the drilled finger hole 'just incase'. Because the failure of the lower tailgate to unlatch is now becoming frequent I've had another look and the rod going to the right hand latch is not moving quite enough to release the latch. Is there an adjustment I can make ?