Speaking to The Telegraph after Sir Keir was led away by his entourage, Paul Stoner explained why he had made the unusual offer.
The 60-year-old said: “I asked him if he wanted an apple and when he said ‘yes’ I gave him a lemon because I think he’s a bit of a joke.
“If you call someone a lemon, you think they’re a bit of an idiot, a little angry.
“He did not even realize it was not an apple. He just looked confused and said ‘thank you’.