Diesel specialist recommendations, Surrey/Hants?

[Tim in Frimley]

My diesel Qashqai has an idle issue which Nissan, God bless 'em, absolutely refuse to recognise as a fault. Basically the idle speed drops *very* low when the car and/or the weather is cold and you come to halt at, say, a junction. Well, it never used to do it, no other diesel car I've ever driver has ever done it and it makes it miserable to drive - its a real fault. If the a/c is off the problem is much less pronounced.

Anyway, I'm not really looking for a discussion about the fault, what I need is to find someone who understands modern diesels who can have a look and give a proper opinion. Relying on plugging it into diagnostic kit isn't the answer, no faults are logged. It seems to me like idle compensation or even an air leak but it could be a hundred other things. It needs an experienced eye.

Any recommendations, around Camberley/Farnborough ideally or out to Woking/Guildford gratefully received!