The new US ambassador to Britain has described a conversation with Margaret Thatcher on a boat as "the best two hours I've ever spent with anybody".

Woody Johnson said the late prime minister was "one of my favourites" as he spoke about famous alumni who had taken part in US-UK educational exchange programmes, remarking on their importance.

Recalling the trip to an army football game in West Point, New York, he said: "She was sitting at the front of the boat by herself and I said, 'Prime Minister, is it OK if I come and join you?', and she said, 'Come on up here'.

"So I spent two hours with Margaret Thatcher and it was probably the best two hours, definitely the best two hours I've ever spent with anybody."