25k in 5 years? I suggest you borrow it, fill it with super, and give it an enthusiastic work out!!

Thanks "Eleckie" and RichardW for your replies.

Dad emailed the VW specialist that did the MOT today. They advised him not to worry about it, but to give the car some decent runs before the next MOT. Think some super unleaded beforehand is a good call too.

Incidently, have had experience of a Kia Pride failing on emissions at one MOT station, then driving to another one, and it passed (This was around 1995).

Though I'd give an update as a year has passed since I started this thread, and the Golf has just passed another MOT.

This year the Lambda reading was much healthier at 1.002

No work has been done to the car, since the previous MOT (not even an oil change).

The last couple of fills have been with super unleaded.

The past 3 weeks the car has had some longer runs (only around 15 miles though). Also, during the same time, my dad has tried to cruise in 5th gear (rather than 6th). The revs have been around 2400 max.

I've seen the term "Italian Tune Up" mentioned on this forum to solve exhaust emission issues. To me, this implies thrashing the living daylights out of the car. This car has never been thrashed.

This years MOT was done at a different MOT station, so it might be down to something as simple as a different exhaust gas analyser, Or, perhaps the test was carried out on a hot engine this year and a cooler one last year?

In any case I'm glad there wasn't any issues.