When mine did it, it was 3 things, so took me a while to work out.
In my case, not only was the turbo leaking oil, but because of some scoring in the centre two piston walls, I have quite high chankcase pressure, and to make this worse, the blowby control valve had failed allowing the turbo to suck the oil vapour from the rocker cover at higher revs, where it would then re-condense in the rubber air tube that runs from the filter to the turbo. This tube has lots of little dimples inside, so it builds up a fair amount of oil over time, where it would then trickle to the bottom of the tube, especially when everything was up to temp, and oil was nice and runny, build up into a deep puddle where the tube joins the turbo, and then the trigger was normally braking as I was facing up hill, where the oil would pour into the turbo, and therefore be fed into the engine.
It did it a couple of times at junctions, but the worst was going up Riegate hill on the M25, where I was already going at just under 70, as everything in front of me started slowing down, my car suddenly started to accelerate hard and all the vehicles behind me disappeared in a huge cloud of smoke. Weird feeling when you car decides to drive it's self!
A new turbo, part fixed it, but then I discovered the issue with the blowby control valve, and put an oil catch can in, which drains back into the sump, and that stopped it completely.
Luckily my engine survived it.
Good luck mate, it's a scary feeling.