Cameron's day: Baby on the way, country to run – and he's moving house

Paul Vallely tells the story of the Prime Minister's first day in the new job

When David Cameron opened his front door early yesterday he could have been forgiven for forgetting that British politics has entered what supermarket marketing men might call its BOGOF era: buy one ruling party, get one free.

There on the doorstep was his delivery of the papers, in a blue plastic sack. All carried a picture of him and his wife on the step of 10 Downing Street. The Daily Telegraph got so over-excited it used possibly the largest headline in its 200-year history to proclaim "Cameron, PM" in letters that looked more than two inches high. But few newspapers, he would have been relieved to see, managed to squeeze in a significant reference to his coalition partner, Nick Clegg.

So the new PM had a spring in his step as he climbed, with a modest smile, into the armoured prime ministerial limo that had pulled up in front of his smart North Kensington (it's not Notting Hill, he insists) address.

Just before 8am he arrived for work at Britain's most famous address. Inside the maze of offices which lie behind the simple black door of 10 Downing Street he was safe enough from the 7,000-word broadside unleashed by his party's leading blogger, Tim Montgomerie, lambasting the campaign which had failed to win the Tories an outright majority. Mr Cameron's silence on immigration, the ConservativeHome website complained, was "like keeping Wayne Rooney on the bench until the last game of the season".

Little did the new Prime Minister care. He was well underway with the business of appointing his Cabinet by the time that Nick Clegg arrived in Downing Street at 9.42am. He slipped on his jacket and went to open the front door personally to welcome his new deputy. All broad smiles and handshakes, the two men posed for the front pages of the following day's papers. At the end the PM placed a friendly arm on Mr Clegg's shoulder, as if to assert his matey seniority. Annoyingly Mr Clegg flung his arm around the Cameron back just before the door closed. One all.

As the morning progressed a crocodile of soon-to-be cabinet ministers made the short walk up Downing Street. The Tories saw the PM first and his deputy second; the Lib Dems did it the other way round. On the telly the pundits were beginning to complain that the appointees were all white middle-aged public schoolboys just as Mr Cameron sent for Theresa May. He made her Home Secretary, Minister for Women and Minister for Equality, a tribute to the legendary female power of multi-tasking, though an odd choice for the diversity portfolio given her voting record on gay rights. Presumably she can give the glass ceiling a bit of a clean while she's up there.

But this wasn't a morning for niggling. "It's like being at a wedding," one backbencher mused. "It would be rude to talk about the chances of divorce."

Boris Johnson was more oblique. As the ministers trickled in and out, the Mayor of London described the new coalition as a mongrel cross "between a bulldog and a chihuahua". Somehow he made it sound like a compliment.

By now the foreign dignitaries were phoning. First Angela Merkel, with some handy tips on how they do coalitions in Germany. Then 15 minutes with Chinese premier, Wen Jiabao, and the prime ministers of Ireland, Italy and Japan.

The cabinet appointments had not been finished before it was time for the first Cameron/Clegg press conference. It was a glorious spring day, with blazing sun and birds singing, so they decided to have it in the Downing Street garden. The posh golden indoor seats outside made it look like a wedding. But it's a bloody thing, the English weather. Just as the happy couple came through the french windows from the Cabinet Room the sun went behind the clouds and a chill descended.

Undeterred, the partners bounced lightly past the wisteria and down, nicely in step, into the garden. Political Jedwards, they wore different-coloured ties so the ignorant could tell them apart. Mr Cameron was marginally the taller, but Mr Clegg, a Tory pundit cursed, looked more at ease, handsomer and distinctly less chubby. Drat.

This may have been a shotgun wedding, but the couple were determined to convince us that they really have fallen in love. The body language was carefully co-ordinated. So too was the joshing – about past gaffes and future by-elections. The sense of double-act was so overwhelming that hacks all around were reaching for comedy comparisons: TweedleCam and TweedleClegg, Fry and Laurie, Morecambe and Wise (though they looked like a couple of Erns). Ant and Dec was my favourite, since I can never remember which is which; perhaps they should wear ties, too.

They took a few questions, but not many. This is, after all, a new kind of politics. And then they went back in to their new National Security Council, at which Mr Cameron said Mr Clegg would be at his side, though, of course, he, as Prime Minister, would chair it.

At the House of Commons, David Miliband announced that he would stand for the Labour leadership. The bookies make him 2/7 favourite. But you can get 7/1 on his brother Ed. Back in Downing Street things have yet to get that fratricidal.