LONDON — A few weeks before last November’s presidential election in the United States, Matthew Barzun, the country’s ambassador to Britain at the time, hosted a party.

When all of his guests had arrived, Barzun clinked a glass and asked for silence. A confidant of the man who had appointed him, President Barack Obama, he said he knew that — whoever won the election — this would be one of his last chances to host such an evening.

So, he said, he wanted to use it to celebrate something that he, and particularly his children, cherished: the special relationship between the United States and English soccer. This was the first time, he joked, that his children had been disappointed that they were not allowed to stay up late to join the party.

No wonder. Barzun’s regular soirees at Winfield House — the sprawling, opulent mansion in Regent’s Park that serves as the American ambassador’s residence — had won no little fame; he knew how to put on a show. This was no exception. The main hall had been covered in artificial turf. The Premier League trophy was on display. In an ornate side room, an Xbox had been set up, offering guests the chance to try their hand at the latest edition of the popular FIFA video game.