Lord Harrowby's house was connected with another stirring event - the news of the battle of Waterloo.
An interesting account of the incident was given by Lord Stanhope, who received it from Arbuthnot. The latter was sitting in his room at Downing Street after returning from the House of Commons, when he heard a commotion in the street below.
On going down to investigate, he saw a carriage and four horses at the door of the Colonial Office, with a number of French standards sticking out of the windows, and Percy, who had brought them, inquiring for Lord Bathurst.
Arbuthnot happened to know that Lord Bathurst was dining with the other members of the Cabinet at Lord Harrowby's in Grosvenor Square, so he got into the carriage with Percy and drove there.
On their arrival, the sight of the trophies caused a large crowd to assemble, and Arbuthnot went out to the head of the staircase, by direction of Lord Bathurst, to declare the great news.
He is said to have announced the total destruction of the French army, when Lord Harrowby, in his usual critical way, corrected him by saying: "Not exactly. I think you are going a little too far."