Irish border: Tory tensions mount as Brexiteers warn against Brexit U-turn on customs union
Pro-Europe Tories have accused Brexiteers of "sabre-rattling" over a leadership challenge risk for Theresa May.
Former Cabinet minister Nicky Morgan, who is behind a pro-customs union Commons motion set to be debated this week, accused Conservative opponents of "hysteria".
The remarks follow a big Government defeat in the House of Lords on the issue of retaining a customs union with the EU last week and reports the Prime Minister and her inner team are considering a rethink on the matter.
One senior Downing Street aide told the Sunday Times that in a meeting last month it was said that Mrs May and her team "will not be crying into our beer" if Parliament forces the Government's hand on the issue.
Such a U-turn would be popular with business leaders and go a long way to resolving Mrs May's difficulties in dealing with the Northern Ireland border issue.
However, it would also be hugely controversial with senior members of the Cabinet, with Downing Street now believing International Trade Secretary Liam Fox and Foreign Secretary Boris Johnson could both resign.
Chairwoman of the Commons Treasury Committee Ms Morgan said her pro-customs union move was not intended to pose a threat to Mrs May and her grip on power.
She told the BBC: "That risk to the Prime Minister's leadership, all this sabre-rattling... is not coming from the section of the party that I represent.
"It is coming from the pro-Brexit section of the party and it's deeply unhelpful.
"If every time Parliament debates these issues, or passes an amendment, or anything like that, all we end up with is hysteria and leadership speculation, that really is not in Britain's interest.
"I think that, actually, the majority of the Conservative Party would not entertain a leadership contest at the moment."
Justice Secretary David Gauke said the Government needs to make the case to MPs for leaving the customs union as part of Brexit.
He told the BBC: "The job of those of us in Government is to persuade Parliament that the route going forward (is) leaving the customs union, but ensuring that we don't put in place unnecessary barriers to our trade with the European Union."
Labour's shadow foreign secretary Emily Thornberry insisted remaining in a customs union "makes sense".
A Downing Street source said Mrs May, who faces the possibility of further Brexit defeats in the Lords this week, would continue to argue for Britain to leave the customs union, adding: "Government policy hasn't changed, we are leaving the customs union."
While the motion backed by Ms Morgan could prove embarrassing for the Government, a meaningful vote on customs union membership is not expected until the Trade and Customs Bill returns to the Commons.