In 1940 my much older cousin, Dennis, an army sergeant, returned to England with the rescued British expeditionary force, from the beaches of Dunkirk.

His family knew he wasn’t far away, in one of numerous temporary camps in Yorkshire, but they didn’t know exactly where, so his mother sent his 20-year-old sister Kathleen on the bus to find him, carrying with her a homemade fruit cake.

Now in her 80s, Kathleen tells the story of her search and eventual reunion with Dennis with magical skill, every detail still vivid in her mind. There are moments of sheer comedy, as when fellow passengers on the bus competed to tell her how many army trucks had appeared in a particular area - “And the bus had all these posters up warning people against loose talk that might help the enemy!”

Then, finally, comes the “not a dry eye in the house” moment when her brother, having been rescued from neck-deep water by one of the legendary Dunkirk “little ships”, is confronted by his sister, carrying one of his mum’s fruit cakes.

Why tell you all this? Because Kathleen’s grandson, who retold the story at school, in a history lesson, was awarded three merit marks, which is unheard of.

It’s a reminder that first-hand accounts such as Kathleen’s are pure gold.

They’re filled with the emotions and the otherwise unrecorded detail that you don’t get in a text book.

Kathleen’s grandson is fortunate in having a grandparent who is old enough to have been a young adult in 1940, and also to have a teacher who could see what this might produce. Such opportunities grow more rare with the passing years, and it’s important to watch out for them and catch them before they disappear.