Buckingham Palace said that the Queen was not in the building when the man tried to get in, but would make no further comment.
More top news
Prince Harry has waved goodbye to the people of Australia after a one-month attachment - meaning he will soon be united with his new niece.
Nearly a quarter of children in the UK under the age of five are overweight or obese, according to researchers.
Answers to some of the most regularly-asked questions about voting in the General Election.