I have recently installed a complete new stainless exhaust (inc.manifold), purchased from APH Performance Engineering Ltd. of Banbury. The owner apparently acquired the jigs and drawings from CTE advanced tech.
The cost was reasonable (slightly less than others), the workmanship excellent and the speed at which the work was carried out was very good (about four weeks).
The exhaust is now fitted, it is not loud but has a pleasing sound and the performance is seemingly better than the standard (although no figures to back that up). It could be that I'd forgotten how quick these cars actually are!
I can thoroughly recommend this firm.