Marilyn Monroe would have approved. The Seven Year Itch, argues Germany’s most glamorous politician, could be cured by making marriage vows valid for only seven years, thus legislating away what is regarded as the most unstable phase of a relationship.

The proposal to turn marriage into a kind of time-share arrangement has shocked Germany. It comes from Gabriele Pauli, who is running to become head of the Bavarian conservative Christian Social Union (CSU) party.

“Many marriages survive only because people think it gives them security,” Ms Pauli told a news conference in Munich. “But only love should count.”

Her idea would apply only to civil marriages. Vows sworn on the altar, “till death us do part”, would not be amended. Civil marriages would be regarded as a limited seven-year contract. “After that initial period each partner would have to say ‘yes’ again in order to prolong the marriage,” she said. “If they do, there is no reason why marriage should not end up as a lifelong partnership, but in the meantime we will have saved the financial and emotional cost of many divorces.”

The Seven Year Itch - the supposed urge to stray into adultery – was a fixture of advice columns long before Billy Wilder made his 1955 film of the same name starring Marilyn Monroe as the blonde temptress of a bored husband. The subject matter was deemed so sensitive by Hollywood that the extramarital romance was played out only in the head of the protagonist, acted by Tom Ewell.

Since then agony aunts have also identified the Two Year Bloat (when complacent husbands start to put on weight), the Fourth Year Slip (when office co-workers start to look more attractive than one’s partner) and any year after the birth of a child as being as perilous to marriage as the seven-year restlessness.

Johann Reisel, head of Catholic marriage counselling in Bavaria, said: “It sounds to me like renewing a mobile phone contract,” he said. “This is just a random number; statistics show that marriages tend to last either three or four years, or significantly longer than seven years.”

Although conventional wisdom is that every third marriage in Germany ends in divorce, the reality is worse. By one calculation, 43 per cent of marriages in western Germany (including Bavaria) end in divorce. In 1970, only 15 per cent ended this way.

Catholic bishops called yesterday for Ms Pauli to be thrown out of the CSU. So too did Edmund Stoiber, who is head of the party and prime minister of Bavaria until next month. Mr Stoiber is standing down from both posts after a campaign by Ms Pauli. Her rivals have seized on her comments as evidence that she is unfit for office.

Ms Pauli is determined to shake up the party, which has ruled Bavaria for the best part of six decades. She posed for a magazine as a dominatrix, and is often photographed on her motorbike.

She has been married twice. Her second marriage ended in divorce last February. It lasted seven years.