I was working in Morecambe on Easter Bank Holiday Monday and suffered a flat tyre as I drove up there on Sunday night.

Forty minutes later, I was congratulating myself on emptying my boot and wrestling with jacks, locking nuts and spanners – not to mention surviving changing a wheel on the open road (mercifully it was the rear nearside).

Then I spotted the yellow writing on the wheel hub that read “Maximum Speed 50mph”.

The tyre seemed exactly the same size as the one I had removed and actually looked in better condition, being unused and not squashed flat or looking the worse for wear.

Logic suggested that there was no reason to drive any slower than I would usually on the M6.

But the certainty that I would be caught if I was breaking any law by driving faster than 50mph persuaded me to restrict myself to the inside lane and obey the wheel’s instruction.

Driving at 50mph on a motorway is not only almost impossible to do, but also does not go down that well with drivers of other vehicles that want to do 60mph in that lane.

Mercifully it was Easter Sunday night and traffic was unusually light otherwise I would have had a succession of HGVs attempting to hop into my boot.

I turned off at a service station and did a bit of online research and could find no certainty about either the validity of the instruction, its legal force or the reason for the restriction.

The tyre’s identification numbers were the same. It was not a space-saver narrow thing.

But I didn’t want to take the risk of finding myself with points on my licence, so I soldiered on, delighting for once that a large chunk of the motorway was reduced to 50mph through endless roadworks.

Having eventually reached my destination, finding somewhere open to replace my tyre proved predictably problematical. But eventually I did, some miles away.

The fitter looked at my spare and said that as it was absolutely identical to the others on my car, the only reason he could suggest for any restriction was that it was a steel wheel whereas the others on the car were alloys.

He went on to make some remarks about manufacturers being litigation averse and covering themselves. If professional fitters aren’t sure, how are we supposed to know?