When I saw the results of the British Social Attitudes report last week, it occurred to me how difficult it is to keep a long-term relationship going in these turbulent times. The report, which has been running since 1983, is significant because it has proved to be a good barometer of social changes and informs social policy.

This year it tells us that married couples are no longer seen as the “norm” and that two-thirds of people see marriage and cohabitation as indistinguishable. Most people now see a wedding as an excuse for a party rather than as a declaration of lifelong commitment.

I must admit that I have some sympathy with this view. Although married myself, I have always felt somewhat ambivalent about a legal document sealing an emotional commitment - and positively repelled by the money made by lawyers undoing that legal commitment when couples divorce, feeding on people’s personal tragedy.

However, it appears true that couples who choose to live together rather than marry are far more likely to break up before their children are five than their staid, married contemporaries. And in my experience, marriage makes a difference for children. They like being part of a solid family unit where everyone has the same name.

Marriage was invented - by men, I’m sure - at a time when life expectancy was much shorter and “till death us do part” meant until the age of perhaps 40. There was no expectation of continuous joy, happiness and sexual contentment stretching over decades. We expect so much of our relationships now.

When I was a child we lived on a rickety houseboat on the Thames. We had very little money and for a long time we all shared one space, without even any wooden partitions; I slept on a camp bed under the piano.

It was a happy, slightly crazy childhood and it’s only as an adult that I have come to realise how difficult it must have been for my parents. There was no privacy. Looking back, I wonder how they ever argued or made love.

They were a difficult combination. He was a naturally solitary type, she more volatile and outgoing. My father was often away, being a naval officer, and perhaps it was those separations that kept the marriage alive - that and the fact that they really liked each other.

My father died when I was 13 and my mother later remarried, to a man much more like her in temperament and who was the most wonderful stepfather imaginable. They were very happy but kept their separate homes, she on the houseboat and he in a house nearby, and could retreat to their own space whenever they wanted to.

Again, perhaps, that element of separation kept things fresh and it’s a lesson I’ve carried into my own marriage. I have always felt the need to escape every so often - to go off trekking through the Himalayas or racing across the Arctic. If you need time to yourself, the sky won’t fall.

Over the past few weeks I’ve been appearing in Ingmar Bergman’s Scenes from a Marriage - directed by my husband, incidentally - at the Belgrade theatre in Coventry and it has been fascinating to see the intensity of discussion these universal themes of love, marriage and fidelity provoke.

Bergman, five-times married himself, dissects the disintegration of a “perfect” marriage in the most forensic way. A friend who came to see the play insisted on taking away a script to study so she would have the best lines at the ready the next time she had an argument with her husband.

Bergman describes marriage as “two people inextricably drawn to mutual misery”, but that is the bleakest view possible. While any marriage does involve tedium and habit - intolerable for those who thought their lives might be extraordinary in some way but turn around one day to find themselves caught in the banal - it also offers the solace of worked-on friendship and the joy of being known profoundly.

Relationships are essentially about bringing home stories and sharing them, so one of the essentials is having something to say. If you are not inclined to go roaming the Masai Mara, that’s where Radio 4 comes in. If life is about sharing and conversation, there’s plenty of fodder there.

Keep thinking and changing: I once had a French boyfriend and was madly in love - or so I thought. We did everything together. For the first few years we spoke French, then I taught him English. Then the magic disappeared. We had become too alike, too repetitive. We had become each other, in effect, and we were bored.

And although life is about conversation, there are some things that should be left unsaid. Bergman suggests those things should be left “in the half-light”. In the play, one of the most devastating moments comes when the husband tells the wife how the sight of her eating an egg at breakfast every day repels him. Judging when to speak and when to stay silent is an essential in a marriage.

I am from an older generation with one foot in the past. I remember my parents’ generation where monogamy and unrelenting stability - yes, maybe tedium - were applauded. Now nobody gives you a gold star for monogamy. We live in a world where young girls have “f***-buddies” and moral values are tumbling.

People are still shocked when a marriage breaks up but - given how difficult it can be to sustain a long-term relationship - instead of being disappointed with those who fail, we should celebrate those who make it work.

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