Very good to hear the diesel was quiet at idle, because it's not a given these days. I recently drove the new Audi A1 1.6Tdi Sport, I had it for a couple of days. I was extremely surprised at how noisy it was when cold or idle, far more noisy than any diesel I have driven in the last 10 years... very disappointing.
I was interested in the A class too, don't understand why Merc can set pricing for the rest of Europe but not UK yet. If you do a basic sterling conversion from the french pricing, the entry level A-class 180cdi should be about £21,500. I've read somewhere it's got a Renault engine, doesn't sound very premium?!? With only a few extras it puts the car out of my budget.
With your observations of the V40 having a better quality interior than the Merc, it's just more evidence that the V40 is better value for money.
It's all very reassuring that I'm making the right decision going for the V40.