The government says it will consider allowing heterosexual couples to form civil partnerships - but only five years after gay marriage has been introduced.
The government tabled an amendment on Thursday night setting out the plans ahead of same sex marriage legislation returning to the Commons next week.
It will pave the way for civil partnerships to be extended, or, if demand has plummeted, scrapped altogether.
Critics attacked the government for stalling on the move.
Gay rights campaigner Peter Tatchell said the delay was a "sad betrayal of the principle of equality".
Culture Secretary Maria Miller said: "The Equal Marriage Bill is about extending marriage to same-sex couples.
"Questions have been raised about whether we should also extend civil partnerships to opposite-sex couples.
"There are strong views on both sides of this debate, and we have listened to those views.
"We are therefore offering the House the opportunity to have a review of this area, rather than legislating now without the required evidence."
The Marriage (Same Sex Couples) Bill returns to MPs on Monday and its passage through parliament is expected to remain bumpy.
It is unlikely that couples will be able to take advantage of any law change until well into next year, with the review of civil partnerships then likely in 2019.
Tatchell added: "While the government's promise of a review of civil partnership law is welcome, it is unnecessary.
"A majority of the public support the retention of civil partnerships and want to make them available to heterosexual couples, according to the government's own public consultation last year.
"David Cameron and Maria Miller should stop delaying and making excuses.
"They say their support for gay marriage is based on a commitment to equality, yet they are refusing to support equal civil partnerships for heterosexual couples.
"They're not being consistent."