The government has been accused of being in contempt of Parliament after ministers refused to lay out how they would respond to a unanimous vote in the House of Commons that declared ISIS' atrocities as genocide.

The accusation was made by the Catholic peer Lord Alton, who has spearheaded the campaign to recognise the treatment of Christians, Yazidis and other minorities by ISIS as genocide.

He told human rights minister, Baroness Joyce Anelay, the government would almost be in contempt of Parliament if it said Wednesday's vote by MPs was "non-binding and that they have no intention of following the will of Parliament in taking this matter to the Security Council".

His comments on Thursday came after the Commons voted by 278-0 in favour of a motion that declared ISIS' atrocities genocide and called on the government to refer the matter to the United Nations Security Council. The vote was historic because it is the first time MPs have declared an ongoing conflict as genocide.

Ministers and ministers' aides were ordered to abstain from the vote and foreign office minister Tobias Ellwood maintained the government's line that it was a matter for international courts, and not governments.

Lady Anelay did not repeat Ellwood's response but insisted the government was doing all it could to compile evidence of war crimes. She did add any specifics.

When pressed on why the government was not willing to make a referral to the UN, which could then confer power to international courts, she said she had to be sure of securing agreement at the UN. She added the government was "not confident" this agreement exists.

She repeated Ellwood's argument on Wednesday that the government had made a referral about the situation in Syria in 2014 but it had been blocked by Russia.

However Fiona Bruce MP, who tabled the motion in the Commons, told Christian Today the referral in 2014 was on a "completely different issue".

That instance was "not about the genocide of Daesh [ISIS] which in my view no country would condone," she said after the debate.

"I believe the referral should be made without comparison to 2014 and am confident it will not be vetoed."

David Burrowes, another Christian MP who spoke in favour of the motion added: "It is about the principle."

He told Christian Today: "Just because there is a prospect of a veto it does not mean you do nothing. Just because it may be challenged, it can't mean you do nothing.

"Once the threshold of genocide has been reached, as it clearly has, we have an obligation."