Even though I scoped the crank and cam sensors and checked it against the trace in 'waveform' forum I thought the timing was ok.

I decided to remove the cam cover and actually check the cam timing using the cam and crank locking tools and found that the inlet cam was out of alignment by only a few degrees.
I also noticed that a new chain tensioner had been fitted, maybe the stretched chain had pulled the inlet cam out of alignment?
Carried out cam timing adjustment and the emissions are now good, Lambda 0.997 at fast idle etc.
We will be recommending a timing chain replacement in the future.

Thanks for all your comments, much appreciated.

Martin.