As Queen, she has had little opportunity to get to grips with the mundane reality of modern supermarket shopping.

So when she was taught to use a self-service scanner today, she only had one question on her mind: could it be tricked?

The Queen, who was visiting a Sainsbury's store to celebrate the chain's 150th anniversary, was given a demonstration of a new till and weighing scale, asking: "And you can't trick it? You can't cheat then?"

Reassured by Damien Corcoran, a regional manager for Sainsbury’s stores in the north east of England, that the weighing scale would catch out any unscrupulous shoppers, the Queen was told how people put items from their baskets on the scales, key in details, and normally pay with credit cards.

When the manager claimed many people liked the convenience of being able to do it themselves, she replied: “I’m sure they do. Everybody wants to hurry.”

Mr Corcoran also showed her how some shoppers now dispensed with tills altogether, choosing instead to pay via a mobile telephone app. “That’s an interesting tool,” the Queen, who is 93, replied.