Traditionally, it has been viewed as a sacred bond intended to last until death.
But many young people now believe marriage should be more like a rolling mobile phone deal, researchers say.
They found that a quarter of 18 to 24-year-olds think marriage should be a temporary contract with a renewal date and the opportunity to “upgrade” to another partner.
A third of this age group also backed polygamy, and 30 percent supported “fluid arrangements”, where people could move between different partners.
Colin Hart, of poll organisers the Coalition for Marriage, said the findings were “deeply worrying”. He added: “Despite all the government rhetoric about the importance of marriage, they are failing to get this message through.”
The poll of 2 002 adults of all age groups also found that almost half back “no reason” divorces, where somebody does not have to justify ending a marriage.
Seventy percent said there should be a statutory cooling-off period before a divorce is finalised to give couples a chance to change their minds.