Diagnostics recommendation

[cirks]

Our Mazda 5 may well have a failing DPF (has required more than one forced regeneration) but I'd like to actually get to the bottom of the issue which may be sensor related too and there is some uneveness in the running of the vehicle at specific speeds.

Can anyone therefore recommend a diagnostics firm in Herts/Beds/North London etc? Ideally, they could also do a rolling road or road test with diagnostics plugged in too