I got time on Sunday so stripped the fuel rail and injectors from the car. I've been putting it off cause I'm not 100% sure this will be the issue... the jury is out. Luckily they came apart no problem, other than getting the "just 1mm too long" stud out holding the fuel rail to the front of the block. I'll get a proper bolt for it. Gave the inlet manifold a bit a clean, although it doesn't look like it int he pic!
I dropped them off today at my contact who has a testing rig. He is cleaning, flow and pressure testing them, so should have an answer whether they are OK on Thursday. I have a set of seal kits which I got from the States, they look about right. It came with the o-ring seal to inlet (smallest one) and a isolator bush, plus another thicker isolator (for a different application?).
So nothing to do but wait, fingers crossed they are OK and were just dirty. Although the new inlet seals should help too. If this doesn't fix it it will likely be the airflow meter, but just going through items one at a time.