This is quite interesting because the symptoms were so subtle.
When I first got the car it was surprisingly rapid if you thrashed it. Lately it has seemed a little slower. Nothing tangible but just a bit slower. Then very recently I've noticed it very slightly bog down under light acceleration. Push it hard and it seems fine. Up hills fine. MPG same as usual.
Checked the leads, DIS, plugs, air filter, MAF, air temperature sensor, all were fine.
Thinking about changing the plugs and air filter just in case....bought some injector cleaner to put in the petrol...
Anyway the exhaust pipe failed big style (pipe to centre box just broke off). Got the centre boxes (thanks to The Boy re: part numbers). Nightmare getting the 4 bolts off... first sheared and had to be drilled out, another came out eventually, gave up on the last two. Then went to casulty to get the metal splinter out of my eye

Had to resort to a garage near work (mistake) but got the exhaust changed. Mistake because they jacked under the wishbones and may have bent one

Back to the story, well the next exhaust sounds a bit more throaty (it is genuine Vx, but slightly different to the original) but f**k me does the car go better. It flies now

. There was exhaust coming out the end of the old one but it must have been strangling the engine.
So if your car doesn't seem quite right and you've checked everything else check the exhaust (not quite sure how though).