What will life look like for Carrie Symonds, Downing Street's 'First Girlfriend?'

Carrie Symonds is not expected to walk into Downing Street with Boris Johnson. Photo / Getty Images

With Boris now on course to become the first Love Actually prime minister, Harry Mount looks at the love lives of former residents of No.10.

Following his election as Tory party leader - and barring any accidents - Boris Johnson will walk into Downing Street this week and achieve his lifelong ambition of becoming prime minister. But will he have Carrie Symonds, the First Girlfriend, on his arm as he strolls through that famous black door?

Insiders suggest she will keep a low profile this week and instead slip in at the weekend, probably by the back door. No 10 looks like a relatively modest prime ministerial house from the front. But it hides a rabbit-warren of buildings – and plenty of back entrances – behind that terraced-house façade.

Whatever approach Carrie Symonds takes to Downing Street – and to her new role – we are in uncharted waters, historically speaking.

There has never been a British prime minister living openly with his girlfriend in Downing Street before – apart from in the Richard Curtis film Love, Actually. Gordon Brown got married in 2000 to girlfriend Sarah Macaulay, just as he was contemplating his leadership bid – even though he only got inside Number 10 in 2007.

Even if Boris did want to do the decent thing and marry Carrie now, he can't. At the moment, he's separated from but still legally married to his second wife, Marina Wheeler.

Of course, there have been FMs – First Mistresses – before. David Lloyd George, the last Liberal prime minister, was an incorrigible Welsh goat, with multiple girlfriends. After the 1935 election, the BBC's Wynford Vaughan-Thomas famously interviewed the old boy in a hotel room, sitting in bed with a naked woman either side of him.

In October 1943, aged 80, Lloyd George married his second wife and secretary, Frances Stevenson. He had been having an affair with her for an astonishing 30 years – during which time he was prime minister from 1916 to 1922. For most of those 30 years, he was still married to his first wife, Margaret.

Lord Palmerston – twice prime minister, from 1855 to 1858 and 1859-65 – was a vigorous swordsman, too. He is reputed to have died in flagrante, aged 80, while he was still Liberal prime minister. At the time, he was seducing a maid on the billiard table at Brocket Hall, his wife's stately home in Hertfordshire. As I played snooker on the billiard table at Brocket Hall last year, I doffed my cap to the great man. It was hard enough potting a few balls on that table, let alone make love to someone less than half your age.

Carrie Symonds is herself reputedly the lovechild great-granddaughter of Herbert Asquith, another amorous Liberal prime minister (from 1908 to 1916). In 1915, during the First World War, Asquith wrote three letters a day to his crush, Venetia Stanley (it's still debated whether they actually graduated from intimate friendship to sex). He even wrote the letters during Cabinet meetings.

But none of these prime ministers openly publicised their girlfriends while in office. Of course, Boris publicly announced he was separating from his second wife Marina in a joint statement in September last year. At the time, the couple, who have been married for 25 years, said that their decision was taken some months before they made it official.

The lack of shock at Boris's young girlfriend is striking – particularly among the supposedly stuffy Tory members who have been voting for him in their tens of thousands. Many of those Tory members – like practically everyone else in the country – will have witnessed the increase in divorces, affairs and mistresses in their own extended families over the last half-century. And they will have become much more relaxed about it all.

There has never been a British prime minister living openly with his girlfriend in Downing Street before - apart from in the Richard Curtis film Love, Actually. Photo / AP

Prime ministers, like all of us, behave in radically different ways. Anthony Eden had a much younger second wife. Clarissa Avon, still with us, turns 100 next year – she was 23 years Eden's junior; Carrie Symonds is 24 years Boris's junior. Tony Blair was the first prime minister to have a child in office since Lord John Russell in 1849. Theresa and Philip May didn't fit the nuclear family model. And so we now have the first Love, Actually prime minister, with a public girlfriend in office.

Northern Anglo-Saxon Protestant puritanism is shifting towards a southern Continental, Catholic, laissez-faire model of behaviour.

In France, people were delighted when twice-divorced Nicolas Sarkozy married the impossibly glamorous Carla Bruni while he was still in office as president.

The French didn't mind Sarkozy's successor, François Hollande, leaving his partner, Valérie Trierweiler, while he was president – and exchanging her for another extremely beautiful woman, actress Julie Gayet. Some say they admire a man going out with a much younger model – it gives hope to all French men. What they didn't admire was the surreptitious, Inspector Clouseau-way Hollande carried out his affair, hopping on the back of a moped, head shrouded in a motorbike helmet.

The same goes for shifts in the moral compass across the pond. Twenty-one years ago, Bill Clinton was impeached – and acquitted – on lying and obstruction of justice charges after his affair with Monica Lewinsky. Now in the White House, we have a president who has five children by three marriages and was caught openly boasting about "grabbing women by the p----".

All around the world, there is a relaxation of moral disapproval. In Leo Varadkar, once socially conservative Ireland has an openly gay Taoiseach.

What you can count on is Carrie Symonds pulling off her new role with media aplomb. She knows her way round Downing Street well, having been communications director at Conservative Party HQ, as well as special adviser to John Whittingdale, when he was the culture secretary, and Home Secretary Sajid Javid. At only 31, she has spent a decade close to power as a political adviser and PR. Downing Street, the beating heart of Britain's power structure, will not be awe-inspiring for her.

Symonds was literally born into the media elite. Her father, Matthew Symonds, was one of the three journalists who helped to found The Independent in 1986, and her mother, Josephine McAfee, was a newspaper lawyer there. One of the other founders, journalist Stephen Glover, writes in the new issue of The Oldie (of which I am editor): "Matthew forged ahead, drawing us in his wake. Without him, The Independent would never have been launched… He's a remarkable person and seems to have produced a remarkable daughter."

There will have to be a careful dance at official prime ministerial events. There is no reason why she shouldn't accompany Boris at Chequers receptions, or at G7 or G20 meetings, when spouses are given their own separate official schedule. Athletes have long taken their WAGS – wives and girlfriends – or HABS – husbands and boyfriends – on foreign trips.

The evolving morals of Western society may not chime with visits to more conservative places, such as Saudi Arabia or the Vatican. But, such is the importance of politeness in diplomatic circles, that it's unlikely any foreign government would refuse access to Miss Symonds.

It's also unlikely that she will give up her Camberwell flat, now famous as much for its nosy neighbours as that red-wine-stain-on-the-sofa row with Boris last month. She is planning to keep her job with the environmental group, Oceana – a useful way of keeping away from the 24/7 pressure-cooker of Number 10.

With a general election possibly in the offing, the south London property could also be somewhere the couple can move to after what might be the shortest ever spell in Downing Street. The current record is George Canning, with a mere 119 days in 1827.

To avoid achieving a new ignominious record, Boris must survive in office until November 21. He may well not make that. October 31st is the big crunch date when, Boris swears, we will leave the EU – a pretty tricky promise to fulfil.

Symonds's spell behind that famous black door could be extremely short. By November, commentators may well be saying of Downing Street, in the words of Sir Cliff Richard: "Carrie doesn't live here any more."