Britain's new prime minister and his young family just can't squeeze into the famous address.
While American presidents live in the spacious White House, British prime ministers are expected to make do with a cramped upstairs apartment that used to be servants' quarters.
But in one of his first moves, Tony Blair, the newly elected prime minister, has indicated that 10 Downing Street is not large enough for his wife and three young children.
Instead, he intends to live next door at 11 Downing Street where Gordon Brown, his chancellor of the exchequer, would normally expect to live. Mr. Brown, a bachelor, is said by officials to be happy with the exchange.
By agreeing to swap houses, Mr. Blair and Brown, who are close personal friends, are breaking one of Britain's most enduring traditions. Prime ministers have lived at No. 10 since the early 18th century.
In doing so, they have put up with cramped quarters. No. 10 is less than a mile from Buckingham Palace, the 600-room home of Queen Elizabeth II. But in terms of living space, it is a universe away. Most of the house is used for official business, and little of it is available as living space for the prime minister's family.
Before the nation voted in the May 1 election, Blair said that he and his lawyer wife, Cherie, along with their three children, planned to live on the top floor of the house at No. 10.
But when the couple inspected the premises last Friday, they decided that even if it were remodeled, the new first family would be in a tight squeeze.
So the prime minister asked Brown whether he would surrender his much larger apartment.
Carol Thatcher, daughter of former Prime Minister Margaret Thatcher, who occupied No. 10 from 1979 to 1990, said yesterday that the house used to irk Mrs. Thatcher, especially in warm weather.
In accord with British political tradition, just-defeated Prime Minister John Major and his family have already vacated the premises. His wife, Norma, was known to escape No. 10 whenever possible. Friends say she found it too confining.