David Cameron is not given to melodrama but he has starred in enough. For the time being, there are three moments of history to remember, outside that famous door. The time when he walked through it with Nick Clegg. The time - even more surprising - that he walked through it on his own, just thirteen months ago.
And now this, which in time will be the only time that mattered. The UK out of Europe. The union with Scotland on the brink. Northern Ireland too. All for what's being called a gamble but is in fact simply a strategic failure.
"I love this country,” he said, his voice cracking. The 74th Prime Minister of the United Kingdom of Great Britain and, more latterly, Northern Ireland. And there will in all likelihood be just one more, before Little England is loosed upon the world.
‘Broken Britain’ is a term that has forced its way into public parlance and the Cameron years - six of them, now over. Well it will be broken, now. And this will be all that he is remembered for.
“I am very proud to have been Prime Minister of this country for six years,” he said, as he strode out into the morning light. “Proud of what we’ve achieved. Keeping our promises to the poorest people in the world. Restoring Britain’s economic strength.”
David Cameron's premiership - in pictures
David Cameron's premiership - in pictures
Britain's Queen Elizabeth II greeting David Cameron at Buckingham Palace for an audience to invite him to be the next Prime Minister on 11 May 2010
Prime Minister David Cameron and his wife Samantha wave from the steps of Number 10 Downing Street on 11 May 2010
On 12 May 2010 Prime Minister David Cameron said in a press conference with Lib Dem leader Nick Clegg, who was then deputy PM, they plan to "take Britain in a historic new direction" and Conservative-led coalition government would be united and provide "strong and stable" leadership
A decade ago, David Cameron visited the Arctic to witness the effects of climate change. However since coming to power in 2010, his government has gradually dropped down a succession of green policies
Prime Minister David cameron told the then New York mayor Michael Bloomberg, the Queen had “purred down the line” after he told her Scotland had voted against independence in September 2014. He was forced to apologise for breaking constitutional convention
Britain's Prime Minister David Cameron greeted soldiers working on flood relief in York city centre after the river Ouse burst its banks, in northern England in December 2015
Claims that David Cameron performed an obscene act with a dead pig and smoked cannabis during his studies at Oxford University spread around the world in September 2015. The extraordinary allegations were made in an unauthorised biography of the Prime Minister written by Lord Ashcroft
David Hartley/REX Shutterstock
In 2016, Mr Cameron was caught up in a worldwide scandal dubbed the “Panama papers”
Prime minister David Cameron and his wife Samantha with seven week old Regan as they meet her parents, first time home buyers Robert Arron and Kelly Jeffers at the Heritage Brook housing development in Chorley, Lancashire. David Cameron has joked that he wants "another baby" and said that he feels a "bit broody" every time he sees a newborn on the campaign trail
Prime Minister David Cameron was criticised for branding refugees in the Calais ‘jungle’ camp as a “bunch of migrants” in January 2016 after thousands of refugees died in their attempt to cross the Mediterranean in 2015
Britain's Prime Minister David Cameron speaks with European Commission President Jean-Claude Juncker during an EU summit meeting on 17 March 2016 at the European Union council in Brussels. Cameron was in Brussels to renegotiate deal of UK membership with other European leaders. The deal, sealed after hours of haggling at a marathon summit, paved the way for a referendum on whether Britain will stay in the EU
President Barack Obama shakes hands with British Prime Minister David Cameron at a meeting at 10 Downing Street in London on 22 April 2016. The President and his wife visited 10 Downing Street where he joined press conference with British Prime Minister David Cameron and made his case for the UK to remain inside the European Union
After David returned from Brussels claiming victory in his renegotiation with European leaders, Boris Johnson announced that he will not support the Remain campaign. The prime minister said publicly he was "disappointed but Boris remains a friend"
Prime Minister David Cameron makes a joint appearance with Mayor of London Sadiq Khan as they launch the Britain Stronger in Europe guarantee card at Roehampton University on 20 May 2016 in London. The 'guarantee card' lists five pledges should Britain remain in the EU, including the protection of workers' rights, full access to the single market and stability for Britain
Britain's Prime Minister David Cameron speaks outside 10 Downing Street on 24 June 2016. Cameron announced his resignation after Britain voted to leave the European Union after a bitterly divisive referendum campaign
It was a highlights reel. Significant achievements, some of them, but all were leading with insidious intent to an overwhelming admission.
“I think the country required fresh leadership to take it in this [new] direction. I will steady the ship for the coming weeks and months.
“There needs to no precise timetable in place,” he said, but “a new Prime Minister should be in place before the Conservative Party Conference in October.”
It is more than ten years since he took over a factionalised and failing party. He transformed it, and now he leaves it as he left it. It is hard not to see how without him, it will always be thus.
As he turned around and strode back through the door, the hair on the back of his head gone grey overnight. The youngest ex-Prime Minister since 1895, drawing his political pension. Yesterday’s man now, when the full peril of tomorrow is when his party will need him most.