Help - Rover engine diagnostics - Bucks/Oxon?

[domster]

Hi guys

I have a running fault on my second car, an N reg Rover 414i K series, which I suspect to be a blocked cat.

Does anyone know any decent diagnostic/K series specialists near-ish to High Wycombe, say Bucks, Berks, Oxon.

I am loathe to take it to my local main dealer as they will charge me 60 quid an hour for a YTS trainee to poke around under the bonnet after their diagnostic machine reveals no fault codes.

Any help much appreciated.
Cheers
Domster