From Wikipedia (for Jno):
"When Tony Blair became Prime Minister in 1997 he chose to reside in Number 11, rather than Number 10, as it has a larger living area; Blair at that time was living with his wife and their several young children, while Gordon Brown, his Chancellor of the Exchequer, was at that point still a bachelor. In 2007, when Brown became Prime Minister, he at first chose to live in Number 11, but soon moved back to Number 10; Brown was by then married but had fewer children than the Blairs.
Following the 2010 general election, the incoming prime minister, David Cameron, moved into 11, instead of 10 Downing Street, because George Osborne chose to remain in his Notting Hill home. In early August 2011, Osborne moved into Number 10.
Prime Minister Boris Johnson and Chancellor of the Exchequer Sajid Javid have continued the recent practice of residing in the flats traditionally used by their counterparts"