Well, took myself down to another local garage today on the hope of getting a pipe stuck up my bum for free, so to speak. Not free, but for £20 they would run through the MOT program on the computer and find out whether my car would pass or not.
Once the car was properly warm we went for it, revved it up to 2500rpm for 20 secs to purge it, then whack the pipe in and see what the HCs come back to in the next 15 secs or so. Answer: 637. It's a pass! Strangely the car had leaned itself off somehow (a consequence of the tappet adjustment perhaps?) and was down to 1.1 on the CO. So I razzed it back up to 2.5 and it didn't seem to have a negative effect on the HCs either.
For the crack I held the revs at 3000rpm for about 30 seconds to see what happened to the HC reading then - came down to 160.
So all told then, it seems that the cams do increase the fuelling a bit at idle, but not to the extent that it won't pass an MOT, or indeed screw up your fuel consumption too badly. I noticed on the drive home that the car was happier pulling from 1500rpm too than it was previously, now nice and smooth down there as well as above 2000rpm.
Huzzah! After multiple attempts of pissing about, it is possible my engine is now actually set up and running correctly? Only Nick T and the dyno will find out in June!