The news that Boris Johnson is living in a rented flat just yards from his family home has raised questions in some quarters about the state of his marriage. But perhaps there is another reason for the unorthodox arrangement: that he and his wife, Marina, are the latest couple to become LATs, that is to say couples who are Living Apart but Together.
It's a growing trend. Research out in 2007 revealed that one in 20 couples chose to live separately. It's thought that more than a million couples now keep separate properties. Of course quite a few of these must be doing it as a way of ensuring their benefits continue. Cohabiting usually results in a loss of benefits and it may be economic to live apart, despite the cost of commuting from one home to another. And it's not a way of living that would suit most people with children simply because it wouldn't be fair .
But most LATs do it because they like it, because it suits both of them to be independent of each other at the same time as having the security of knowing there's always someone "there" for them long-term. It means they can get on with interesting creative lives without having either to consider someone else's feelings the whole time or having the stress of looking for someone to share their lives, with all their spare time taken up in dating, falling in love, falling out of love, and so on that's involved in being single.
Now, of course it's a luxury. In the past this way of living used to be the prerogative of grandees who would often divide up their huge statelies into different wings and live, one in one wing and one in another, virtually separate lives. But now, despite the recession, it's still a sign of more affluent living. Apparently many young couples simply find they have too many possessions, combined, to fit into one home and anyway their decorating tastes are poles apart. In the past people would usually move straight from their homes into marriage, but now most of us move into our own flats or rooms, and create our our personal nests, before moving in with someone else. And that gives us a taste of the joys of independence.
If you're used to the pleasure of having girlfriends round for cosy chats or, if you're a man, having friends around to watch the football, it's nice to be able to do it without having politely to recommend that your partner buzz off for an evening. Once you've got used to being single, it's a wrench to give up all the advantages of living exactly how you want to live.
Perhaps it's a pleasure because more people work at home – and two people working at home all day can be a stress. Even one person working at home, with constant interruptions from family life, can be irritating, particularly if one person has a completely different schedule – either getting up early for dawn flights, or perhaps just having a different time clock. Many's the person who like a good night's sleep who's married to someone who, when they wake at three in the morning, likes to potter about and put on the telly. Snoring can drive people into separate rooms – but even better if it's separate homes. Snoring, as we all know, can penetrate the thickest of walls. And if someone finds they can only get a job in another part of the country when the children are settled in their schools at home, living separately might be a good idea – there are always weekends and Skype to keep the relationship alive.
Then with more women going out to work and leading independent lives, that rather cloying idea of togetherness is on the way out. I always feel sorry for couples who go supermarket shopping together and who insist on sitting next to each other at dinner parties. They seem to live on a different planet. Then there's the question of having been once bitten and twice shy. If living together during their first relationship ended in divorce, why not try, second time around, to beat the jinx by marrying but never actually living together? Then there are no rows about the toothpaste tube, the seat being left up, or who puts out the rubbish.
Finally, there's the romantic argument. Lots of couples just find that living apart keeps the relationship alive. "Absence makes the heart grow fonder" and even if someone's just been living down the road, it's still a compliment when he or she knocks on the door and asks for a date. Living apart means that you are always together by choice. There's no " 'er indoors" about it. And paradoxically, living apart can often bring you closer.
Boris and Marina are not alone...
Brad Pitt and Angelina Jolie
Last year, rumours abounded that Pitt was occupying the main house at their sprawling Long Island estate, rented during the filming of Salt, while leading lady Jolie lived in one of the many annexes.
Woody Allen and Mia Farrow
In the early days of their relationship, Woody Allen and Mia Farrow lived in separate apartments on opposite sides of New York's Central Park. "I think it's because we don't live together and that she has her own life completely and that I have mine that we're able to maintain this relationship with a certain proper tension," Allen said at the time.
Margaret Drabble and Michael Holroyd
The writer of 17 novels, as well as many plays and short stories, lived in a different part of London from her husband, the biographer Michael Holroyd, during the early years of their marriage. In 2005, she said, "living too close can make people unkind to one another".
Helena Bonham Carter and Tim Burton
Bonham Carter and her director partner live in three adjoining, but interconnected, London houses, although she says that they and their children co-exist as one happy family.