IF a woman finds that the kind and considerate man she has lived with for years suddenly stops helping with the washing and bridles at taking out the rubbish, it is probably because the couple have got married.

Academics have found cohabiting couples are far more likely than those who are married to split housework evenly - but after the wedding they revert to stereotype, with the woman taking on the great majority of tasks.

The study argues that the effect holds true even in couples with a strongly egalitarian outlook before they are married, at which point women become less likely to fight for their rights.

“Marriage is generally accompanied by expectations of permanence that may not be the case in a cohabiting relationship,” says the research by American academics to be published in the Journal of Family Issues.

“Cohabitors, therefore, may be more prone to aggressive bargaining when it comes to exchanges of time and effort in the household, and less willing to do more than what they perceive as their fair share.”

The researchers, based at North Carolina State and George Mason universities, took data from more than 17,000 people in 28 countries.

Overall, men averaged 9.41 hours’ housework per week and women 21.13 hours. It found that the higher the marriage rate in each country, the higher the proportion of housework carried out by women.

British men come in 10th place, performing 35% of chores, well below the most egalitarian countries of Denmark, Finland and Norway. The Scandinavian countries, as well as splitting housework more evenly, also have the highest cohabitation rates.

Anna Addison, 30, who lives in Middlesbrough with her husband Paul, said: “When we first moved in, the novelty of living together meant we shared the housework.

“It was the same for the first year after we got married, but when I got a nine-to-five job everything was left to the weekends and I ended up doing it all myself.

“Paul definitely changed after marriage. I do rely on him for some technical things in the house but, for housework, it’s just me now.”

Frank Hanna, co-founder of the Mediation Agency and author of a book on conflict resolution, said: “With cohabitation, to put it bluntly, there’s no contract and the likelihood of a more peaceful relationship is higher than in a marriage. When marriage takes place, the race is over. Men see the requirement to behave as starting to diminish.”