模范夫妻告诉你婚姻天长地久的秘密

"I fancied him for all the wrong reasons," says Jane Fearnley-Whittingstall, eyes twinkling at the memory. "Rob was terribly handsome, which wasn't necessarily a sound basis for a permanent relationship."

After 47 years of marriage she is, she says, lucky that the glamorous Oxford undergraduate turned out to be a kind and thoughtful man who still makes her laugh (and who grows some very fine purple sprouting broccoli). "I don't think we ever run out of conversation," she says, although she happily admits they still have arguments, as all couples do. "Rob will have got over it in five minutes, while I'll be brooding away in my lair for hours and hours."

As you would expect from the author of The Good Granny Guide, Jane Fearnley-Whittingstall, a very young-looking 70-year-old, has her feet firmly on the ground. In her new book For Better, For Worse, subtitled "A light-hearted guide to wedded bliss", she celebrates the institution of marriage while wondering how on earth any of us manages to stay the course.

She talks about the domestic front line – housework, the television remote, snoring – and the vexed issue of in-laws. She talks about flashpoints that signal danger, like financial anxiety, and whether infidelity is the ultimate betrayal. With candid comments from those she has interviewed, and extracts from novels, letters and songs – by everyone from Winston Churchill to the Beatles – she presents a down-to-earth picture of marriage that makes it seem both a source of joy and plain hard work.

Marriage is, of course, very much in the headlines in the run-up to the election, with the Conservatives promising tax breaks and Labour dead set against the whole idea. Fearnley-Whittingstall manages to champion marriage while suggesting tactfully that all long-term relationships are equally valid.

"I don't think that it's the role of government to manipulate people's choices about the way they live their lives. If at the moment the tax system is unfair to married people, it should be evened out, but I don't think it should be made more advantageous to be married." In Britain today, after all, many couples live together without tying the knot: her own children Sophy, 46, and Hugh, 45 (the well-known chef), had long-term relationships with their partners before they married.