A Government pledge to allow straight couples to have civil partnerships is about to be abandoned, a Conservative MP has warned.

Tim Loughton blamed the sacking of Education Secretary Justine Greening in last month’s botched Cabinet reshuffle for the U-turn, with the Home Office resisting the change.

Instead, the Home Office now wanted only a review of the current laws – with no commitment to extending civil partnerships to heterosexual couples.

Pinpointing the sudden departure of Ms Greening as the crucial factor, Mr Loughton told PA: “Yes. That's the nub of the problem, I'm afraid.

"Justine went on record and it was covered extensively and she made a speech and having told me that yes, she supports the bill, effectively.

“I took that as the Government's support for it and there was no rowing back when it went public in the press.”

Ms Greening’s sacking left the issue with the Home Office, Mr Loughton said, adding: “The cautious Home Office officials have been raising questions as to why you can't do it rather than finding ways of making this happen.”

A Government spokesperson later appeared to confirm the U-turn, saying: “It is right that we evaluate the demand for civil partnerships before we make changes to the law.

“We continue to keep this under review and are assessing the demand for civil partnerships amongst both same sex and opposite sex couples.”

Civil partnerships were introduced in 2004 as an initial step on the road to legalising gay marriage.

But some straight couples who do not want a traditional marriage have argued there is now inequality in the law, because they do not have the choice of a civil partnership.

Mr Loughton has put forward a Civil Partnerships, Marriages and Deaths (Registration Etc.) Bill, which will be debated by MPs on Friday – but which is now poised to be watered down.

However, the former minister said a court could yet force ministers - “kicking and screaming” - to reinstate his plans to extend civil partnerships to mixed-sex couples later in the bill's passage through Parliament.

In May, the Supreme Court will hear the case of a heterosexual couple fighting for the right to enter a civil partnership in the middle of May, Mr Loughton said.

Rebecca Steinfeld and Charles Keidan want to secure legal recognition of their relationship through that route, but are prevented because the Civil Partnership Act 2004 says only same-sex couples are eligible.

The academics, who live in Hammersmith, west London lost a battle in the Court of Appeal on the issue.

But judges said they had established a potential violation of Article 14 of the European Convention, which relates to discrimination, taken with Article 8, which refers to respect for private and family life.