Openly gay Conservative MP Mike Freer has spoken out to say that he thinks other Tory MPs are trying to “derail” the equal marriage bill, and that an amendment to allow opposite-sex civil partnerships could undermine it.

The review has been tabled by the government as an amendment to the Marriage (Same Sex Couples) Bill, which will reach its report stage in the House of Commons next week.

Mr Freer, the MP for Finchley and Golders Green, who is in a civil partnership, spoke out as a group of Tories expressed that they thought they could succeed in amending the bill to extend civil partnerships to straight couples.

Speaking to the Guardian, he said he thought doing so appeared attractive, but that it would bring “practical difficulties”. He went on to say he agreed with Culture Secretary Maria Miller, who ruled out the idea as current government policy, on Tuesday.

He said: “I think the original amendment to extend civil partnerships to heterosexual couples is superficially attractive. But there are some practical difficulties about how this would be implemented. Maria Miller [the culture secretary] has been quite right to say there is a valid point but we need to look at it in a bit of time to see how civil partnerships bed down post equal marriage.

“There is always a danger that some people who are moving some of the amendments are not seeking to be helpful but actually seeking to derail the bill and hiding behind superficial ‘helpfulness’. That is why Maria Miller has been very careful and cautious in saying: ‘You have raised some interesting points and perhaps we do need to look at this but this isn’t the right bill to do it. Let’s see what happens after the bill passes and come back once we have seen how things pan out’.”

He went on to say that he thought that some Tories, posing as trying to help the bill, were attempting to scupper it, and further emphasised his agreement with Ms Miller.

“There is always a danger that some people who are moving some of the amendments are not seeking to be helpful but actually seeking to derail the bill and hiding behind superficial ‘helpfulness’. That is why Maria Miller has been very careful and cautious in saying: ‘You have raised some interesting points and perhaps we do need to look at this but this isn’t the right bill to do it. Let’s see what happens after the bill passes and come back once we have seen how things pan out’.”

Tim Loughton, the Tory Children’s Minister, who tabled the amendment, rejected the claim that he was trying to derail the bill.

“It is absolutely not a wrecking amendment. It is getting a huge amount of support from people who are passionately in favour of the bill. They clearly wouldn’t be supporting it if they thought it was a wrecking amendment. This whole business of having to delay and consult doesn’t hold water – they have already done that consultation,” said Mr Loughton, who voted against the equal marriage bill in the first commons reading.

Human rights campaigner Peter Tatchell, argued that the review of possibly extending civil partnerships to same-sex couples was “unnecessary”, as a majority of the public already supported it. 

The Church of England also released a statement expressing its opposition to suggestions that the government should review civil partnerships.