Just to update the thread..
Took it round to bill and coilpack changed, nope, swapped for a new spark plug and within 5 mins it was black, all injector seals checked and swapped around but nope.
cylinders 1,2 + 3 all have a noticeable tone when unplugged but 4 makes no difference??
It doesnt missfire like an obvious coilpack gone, but brings a fault code up every so often on cylinder 4 and idles lumpy, as well as the negative deviation code, but it boosts as it should, seeing 14.9 - 15.2 on the wideband guage on idle and 12's under load.
I was stuck in traffic on the m25 (for 3 hours!) and it was really annoying as I had to ride the clutch the whole time as it would judder in 1st, (you know where you're crawling in traffic and you manage to let the clutch all the way out but dont need to accelerate) bill raised the idle rpm by 100 which has smoothed out the rough idle a bit but its still there.
So.... its going to total-vag for a compression test, if that comes back ok then it might point to a wiring fault.