Sarah Sands: Marriages founder on trivia but are immune to the Pope

The initial reluctance of Miriam Clegg to campaign with her husband was cited as evidence of her down-to-earth modesty. She had "got real" about the everyday demands of a working mother. Since then, there have been clues that the balance of power is elsewhere in this relationship.

Only the media refer to Mrs Clegg. She, unlike the other wives of the political leaders, goes by her maiden name, Miriam Gonzalez Durantez. Spanish, she has also declined to take British citizenship. Nick Clegg says that when he met his future wife in Bruges, "I barely understood a word she said for the first weeks, but I thought she was magnificent."

She made herself plain enough after that. The couple's three sons were to have Spanish first names. Nick Clegg took paternity leave after the birth of their first son, so his wife could return to work. Although he is an atheist, Clegg agreed that the children should be brought up as Roman Catholics.

Asked by a journalist about his choice of holiday destinations, Clegg replied: "I have gone to the same village in the middle of Spain. It is where my wife comes from and where my in-laws come from. Miriam has always said – brutally so – that since she lives in this country and has her [sic] children raised here, I can jolly well spend every minute of my holiday there."

So let us not assume for a minute that the woman with the black treacle eyes who co-authored the book Regulatory Aspects of the WTO Telegrams Agreement – well-thumbed, I hope, by her husband – is a surrendered wife.

It is intriguing that marriages can survive deep philosophical fissures in a way that light acquaintances cannot. As the election approaches, tribal loyalties start to harden. There are trigger issues that can end dinner parties at a belligerent stroke. The Tories' "judgemental" bias in favour of marriage. Selection in education. Hunting. The Last Night of the Proms.

The Sun and the Mirror, the Telegraph and The Guardian are irreconcilable. Yet marriage can jog along a faultline as fundamental as faith versus atheism. An atheist was convicted last week of leaving offensive material in Liverpool's airport prayer room because he minded so much. Philip Pullman rages against the Roman Catholic church. Yet Clegg does not take issue with his wife for indoctrinating their children in something he believes to be false.

This is the beauty of marriage. It is a model for peace processes and might even be the blue print for a hung parliament. Fundamental, irreducible differences do not matter very much. John Bercow, the Tory speaker, is sanguine if his wife, Sally, a Labour candidate, calls on voters to sabotage the Conservative election campaign.

I have watched Andrew Gimson, the Telegraph journalist and die-hard Tory fogey, regard his wife across the dinner table with adoring admiration as she announced her intention to destroy the Conservatives.

In the sanctuary of marriage, the personal is not political. Marriages founder over leaking washing machines or division of labour but never over ideology. Indeed opposite views can be an invigorating form of flirtation. A staunch right-wing male friend of mine, consistently chose left-wing female lovers for this reason. Bigotry or meanness matter, but not politics and religion. Polly Toynbee and Simon Heffer could not survive a television studio together, but might have had a very jolly marriage.

Sarah Sands is deputy editor of the 'London Evening Standard'