I’ve just had a fascinating journey with the bloke who could well be the Thames Valley’s angriest taxi driver.

And this wasn’t the stereotypical ‘hang the bleeding lot of them’ rant. Instead I got a good 10 minutes of the guy’s full-and-frank opinion of his ’07-plate Peugeot 407 and, more specifically, the particulate trap warning light that was glowing on the dashboard.

My mistake was to comment positively on the newness and cleanliness of his cab, and its superiority to most of the scrapyard-dodgers that make up Oxford’s private hire fleet.

It turned out that he had only had it for three weeks, and it had already gone back to the garage twice to have its particulate trap reset. And just before he picked me up, the warning light had come on again.

He’d been told that his car wasn’t designed for use in town, and that he should make sure he ‘takes it on the motorway’ every couple of days to burn off the trapped particulates.

But with his custom based entirely around Oxford’s congested urban streets, he was predictably unwilling to spend time and fuel burning up the M40 or A34 to keep the emissions control system ship-shape.

It’s a problem that we’re already familiar with an Autocar – the particulate traps of both our XF and erstwhile Skoda Octavia vRS TDI spat their dummies at an enforced all-urban diet. But until today the obvious negative effects for the taxi market, where drivers can cover tens of thousands of miles while rarely passing a derestriction sign, had never occurred to me.

Anyway, my driver reckoned that he had a solution – a friend-of-a-friend reportedly knows how to ‘fix’ the problem, which I imagine involves removal of the particulate trap for everything except MOT emissions tests.

It makes you wonder just how many particulates are going to be getting trapped by the UK’s private hire fleet in a couple of years time…