Couples without children have happier marriages, according to one of the biggest studies ever of relationships in Britain.

Childless men and women are more satisfied with their relationships and more likely to feel valued by their partner, the research project by the Open University found.

But researchers also discovered that women without children were the least happy with life overall, whereas mothers were happier than any other group, even if their relationships faltered.

The study, involving interviews and surveys with more than 5,000 people of all ages, statuses and sexual orientations over a two-year period, will be presented at the British Library this week.

Saying thank you and giving compliments emerged as one of the most important factor in keeping a relationship healthy across all groups.

Funded by the Economic and Social Research Council, the survey also found that people who had been in a long-term relationship before were more likely to know how to sustain the next one.

The report also said fathers were twice as likely as mothers to cite a lack of sexual intimacy as the thing they disliked most about their relationship.