Looking for a 350z specialist

[Peldrigal]

Hi guys: my 2006 350z failed the MOT because of emissions. The mechanic suspects are the catalytic converters. He also mentioned not being able to putting well up to temperature because the clutch was slipping badly (I was expecting its time might be coming)
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He suggested having a specialist check it to understand what's going wrong: any suggestion about someone within easy reach of the Cheshire/Manchester area with good expertise on these issues?