The Prince visited Waitrose

He met staff and students at Marlborough College before unveiling a commemorative plaque in the grounds.

Mrs Parker Bowles was also present, in her capacity as trustee of one of the participating organisations.

One onlooker, Elsie Peck, said: "I think it's nice to see them together. They've got a life to lead."

Earlier, Prince Charles had surprised shoppers with a walkabout around a local Waitrose supermarket, whose shelves bear some of his Duchy organic produce lines.