Right, I'm fitting my turbo tonight, and when it dropped it's oil, in order to get it up the drive I popped some semi synthetic in, literally 10 seconds running.

Would I be ok to fill it up with semi, let it warm up, then drop oil from the sump, then Change oil filter, and fill up with fully synthetic PD oil?

Yeah; the fully synth stuff is there because it's better able to resist the heat and sheer stresses of being run through the turbo at peak boost on a hot engine.

A 5 min run staying under 1_800 to warm up, drain and replace is no issue.

I was more worried about the cam lobes, as they operate the Injectors? But thanks for the input :-)

What's the spec of the semi-synth, just out of interest? Check the manual for specifics, but IIRC Skoda / VW state that ACEA A1/B1 oil is OK if nothing better's available anyway...