Fixed now (I hope so, touch wood!)

This was a good one. It was probably two (or three) issues pointing towards the similar symtoms, making it inconsistent.

1. The fuel pipe kissing hot bits is a pointer towards lean running
2. The FPR return pipe being kinked to the point of marginal flow, doesn't help fuelling either.
3. The blody CTS sending crap data was the icing on the cake.

It must be a Moronic bug somewhere, because the ECU is meant to ingore data that's out of bounds and/or inconsistent with other readings. It's meant to throw up a fault and use some fixed value to get you home.
In this case it tries to act on the crap data, so no fixed value to save your @rse from embarassment -- full lean on a turbo, regardless of throttle position or boost, for crying out loud...

This is a 'gotcha', needs to be on my site somewhere...