Turns out, the turbo is not happy. Probably not happy that it hasn't been used in... well... forever I guess. Similar to how I feel about the entire car!
The intercooler had about a litre of oil in it. The turbo outlet from the compressor, actually goes into a U-bend, that enters the bottom of the intercooler. This U-bend was full. The car had therefore been drinking oil.
Dropped it all out, put some 10/50 fully synth in there and took the pipes off the turbo.
After all that smoke had calmed down, oil is just pissing out of the compressor housing.
Checked the oil drain - not blocked, correct size and facing perfectly south - enters above the oil level in the sump. Checked blow-by = none. Checked oil pressure = normal. Even compression tested the engine - all uniform on all cylinders.
The turbo is now with AET, for their diagnosis. When I removed it, evidence was there to suggest its come through the turbine side seal as well.
Hopefully it can be repaired cheap enough.