Giving his first interview since becoming Prime Minister, David Cameron described a surreal moment that brought home the change that taken over his life. "The radio went off as I was just waking up in my own bed at home," he told The Sun. "I heard 'This morning, the Prime Minister will ...' and I thought 'Oh God, what's he doing now?' And then I thought, 'Oh no, hang on a second; it's me.'"
There will be many more culture shocks in store for Mr Cameron and his family as they accustom themselves to high-pressure life in 10 Downing Street. Samantha Cameron, five months' pregnant, has already accepted that life cannot continue as before, and has stepped down from her full-time post as "creative consultant" for the upmarket stationery firm, Smythson. She will work two days a week.
The decision will knock a big hole in the family income. Her earnings were reputed to be £400,000, and her husband has just reduced the Prime Minister's salary to £142,500. But the Camerons are not going to be strapped for cash.
In addition to wealthy parents on both sides, they will enjoy their grace-and-favour home in Downing Street and their country home in Chequers. They will probably rent out their £2m home in west London, bringing them an income as the property gains in value. And if two official homes are not sufficient, they can fall back on their £750,000 mansion in David Cameron's Witney seat, bought with a £21,000-a-year mortgage paid by the taxpayer.
In the spacious, airy rooms of Downing Street, where they will spend most of their days, there will always be a pleasant buzz of activity, and always someone on hand to give help. If they need to travel, there will be a car outside, with a driver. If they need to make a phone call, they need not look up the number, because Downing Street's unflappable "switch" is famed for being able to track down anyone, anywhere.
What will be much harder will be the utter loss of privacy. Previous prime ministers' wives have had to cope with indignities such as waking in the morning to find a civil servant by the bed with an urgent message for the prime minister. Even when the family is on holiday, Mr Cameron will never be out of touch with the Civil Service, and there will always be armed guards near by.
Downing Street was almost entirely child-free for decades until the Blairs moved in. Leo Blair, who will be 10 next week, was the first child to be fathered by a prime minister since Francis Russell, son of Lord John Russell in 1849.
The flat above 11 Downing Street – which is larger and more child friendly than the one over No 10 – is empty now, as staff move in to clean it, but the Camerons are expected to move in soon, with Nancy, aged six, and four-year-old Elwen.
The children will have the extensive gardens of Downing Street to play in, and at weekends they can explore the 1,500-acre estate around Chequers, but little about their lives will be normal.
Other children learn independence in small stages, such as being allowed to go to the shops alone for the first time, but not the Cameron children. An adult will have to accompany them whenever they leave the heavily guarded compound around Downing Street, and the police will have to know where they are. From now, the Camerons are a family imprisoned in their privileges.