Well it did it again this morning!
Real bad loss of power like 1 or 2 pistons not firing. Was on the M4 and lost 20mph with my foot pressing harder!
No real jumping, nor misfiring. Could hear some clicking noises, then eventually it comes back and runs normally.
So this is the second time this has happened, first was over a year ago and a similar situation, just after a steep fast climb.
Got no chance of finding that fault!