My wife was telling me something funny this morning.

Our son is 5, and has just started his second year at school.

They start doing PE properly this year, and the school was a bit late telling everyone the children would need a PE kits.

The staff put up a poster to highlight what parents would need to supply.

Kids would need shorts and a T-shirt every Wednesday. The image showed a boy wearing a white T-shirt and blue shorts.

Immediately, Mums who are used to being fully prepared and totally in control of things like this when into overdrive.

Mornings were spent searching for blue shorts and white T-shirts.

No joy in M&S, said one pair who’d reconnoitred the high road.

We heard from others who’d come up short in Crouch End.

T-shirts were being bought in packs of four just for the sake of the one white one.

Gangs of parents at the schools gates were discussing what might come to be known as the great white PE T-shirt shortage of 2011.

One child’s mum was even proclaiming her boy would just have to wear red shorts – and anyway it was ridiculous that the school should expect everyone to go and buy new things overnight.

She was right in principle, of course, but what damage might that do to her child, we all thought.

Eventually my wife was chatting to another mum, who out of nowhere said this:

“I really am stupid, you know. I’ve been searching round for bloody white T-shirts and blue shorts!”

“We all have!” answered my wife.

“But I looked at poster again this morning. It just says ‘shorts and T-shirt’. It doesn’t say ‘blue’ or ‘white’ anywhere!”

At that point, had you been in North London, you might well have heard the collective sound of about 50 hands slapping 50 foreheads, accompanied by groans, “D’oh”s and other self-berating exclamations.

There was indeed nothing in writing to suggest the prescriptive colours mums had so readily interpreted.

Nothing that is, apart from the image of a boy, wearing blue shorts and a white T-shirt.

People’s propensity to fill in the blanks certainly is a force to be reckoned with.

And advertising need not be ‘social’ to become an object that influences the spaces between people.