Hi Gary,
As I thought the DPF was part of the problem. Luckily I had thought of the EGR valves as was said by the AA engineer . I though that the cost would have been about £275, but my mechanic took my car and came up with a different answer which saved the EGR replacement.
His solution was to clean the whole exhaust and he had a mechanic friend who could do the work and de did for £180, My s type is now as smooth as ever!
Regards, Peter.