Thanks Manny and 95 E320cab for your responses. I will certainly advise the forum of the outcome. The MOT analyser supposedly has an inbuilt check system (I am not sure whether the inbuilt check system has a inbuilt check system!). The test was administered by two different mechanics on the initial and retest assessment...so I can exclude individual incompetence.
Suggestions that I have received from a generic CAR DIY site in the UK, suggest that the high Lambda reading is often indicative of an engine rather than CAT problem. Before the second retest I took the car for a 170 mile run with Injector cleaner in the tank and on the day of the test I took it for an 8 mile run prior to the test. Another respondent asked for the other gas details but the emission test in the UK only records the CO, HC, and Lamba readings. I have not replaced the charcoal canister and I probably have been guilty of occasional over fill but I don't know if this would explain the symptoms. It has also been suggested that I check the vacuum hoses. Is the fact that the car easily passed the idle CO test a significant factor in fault deduction?
I appreciate your help...it helps to maintain sanity.
John in overcast England