Allowing your partner to sleep with other people could be the key to a happy marriage, psychologists have claimed.

“Outsourcing” areas of the marriage such as sex to other suitors could make a relationship work in the long run, they argue.

For marriages in which the passion and intimacy has gone, Eli Finkel, from the department of psychology at Northwestern University in Illinois, advises embarking on an agreed “non-monogamous” relationship.

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“It may be that your spouse is a terrific source of social support and intellectual stimulation but you haven’t had sex more than twice a year for the last five years and neither of you thinks that’s adequate,” he told The Telegraph.

“So you could say, that’s one of the needs I am going to fulfil elsewhere. I don’t recommend cheating, but an openly consensual non-monogamous relationship, that may very well be functional.”

In the paper The Suffocation of Marriage, Prof Finkel and his co-authors argue that people now expect more from a partner than ever before – to be a lover, friend, confidant, therapist, and someone to help achieve their long-term goals.

Yet, couples are spending increasingly less time with each other, meaning many are left unsatisfied. He also suggests living apart and placing specific diameters on the relationship.

“In 1800 you didn’t have to have a profound insight into your partner’s core essence to tend the chickens properly or build a sound physical structure out of the snow,” he said.

“In contrast, in 2014 you are really hoping your partner can help you on your voyage of self discovery and personal growth.”