Guess what...... the misfires came back.
This time I did get a code, and the misfire has stayed on cylinder 2. So that rules plugs out in theory.
The more I get these misfires the more I'm starting to recognise a pattern: WOT in 3rd at 2500-3500rpm 'triggers' it. I reckon if I never used full throttle I'd never get this misfire.
Anyway, the misfire seemed to ease somewhat, then I parked up for 5 minutes, tried again, and the misfire was gone.
I'm a bit p*ssed off that it didn't miss a beat with you @Tfsi_Mike. It's all quite perplexing. So, the drama continues. I can at least now rule out both plugs and coils, but I was pretty sure that was the case anyway.