On accelerating onto the carraigeway, the power suddenly died after I went into third gear. Changed into fourth and the power came back, then died again. Changed to fifth and power was back again. It was as if somebody flicked a switch to turn the turbo off.

This could well be heat related? I remember the same thing happened a couple of times last summer but had no reoccurance during the winter months until yesterday.

No errors or flashing lights or anything. Once I was up to speed, cruised along to the roundabout. Power was back again when accelerating away from the roundabout.

Any ideas?

did it sound like it was revving up and not going anywhere whilst you were under power , just thinking it may be clutch slip , probably wrong though i hope

Definitely not clutch slip - although I'm working up to needing a new one.

Any other ideas?

Overboost by the sound of it, you running with a remap? Just dont have lead boots

lol...I am... is there anything I can do about it?

Dont hold the revs too high if you look at the plots off the rollers you will see the power really drops after 4000 so use 2500-4000 and dont totally cane it. Also get the map checked to check that its not spiking on the boost low down, see other post about a knackered turbo.