The Prime Minister is facing a parliamentary defeat on her post-Brexit customs arrangement proposals, and is set to miss a promised deadline for answering questions about the Irish border and trade, sources claim.

Theresa May has repeatedly backed away from decisively answering the Customs Union question, and a group of 12 MPs are now threatening to defeat the government in a vote on House of Lords amendments to the Brexit Withdrawal Bill on the topic, The Times reports.

The Tory rebels believe Mrs. May will fudge the issue and are set to team up with opposition and anti-Brexit MPs to humiliate the government in Parliament, the paper claims. Twelve of the amendments will be voted on next week, on the 12th of June.

Many of the Lords amendments were perceived as attempts to block or frustrate Brexit and include forcing ministers to negotiate a future Customs Union arrangement – removing the option of walking away from talks – and giving Parliament a “meaningful role” after the exit talks.

ITV’s Robert Peston, who has been fiercely opposed to Brexit, was sounding emboldened in a blog post on Monday night about the prospect of Mrs. May being defeated.

“Tonight the odds of her winning look slim – because rebel Tory MPs, led by Anna Soubry, Nicky Morgan, Dominic Grieve, Antoinette Sandbach and the rest, met and think they have the votes to defeat her,” he writes.

“The point is that they, and Labour, and the Scottish National Party all want the UK to stay in a Customs Union.

“And they want a parliamentary vote on whatever Brexit deal she ultimately negotiates with the EU to be ‘meaningful’ in the sense that MPs should be able to instruct her to return to the Brussels negotiating table.”

Tories who once supported the Prime Minister are also turning against her, he claims. Mrs. May’s spokesman has commented: “There are amendments which were passed by the House of Lords which are unacceptable which we will be looking to overturn.”

It is now three weeks until the EU summit at which the EU 27 expects the UK to answer key questions on the kind of customs relationship it wants after Brexit and how it plans to keep the Irish border open.

It has been widely reported that Mrs. May will not answer these questions, and will fail to publish a promised white paper on Brexit before the summit.

Peter Ptassek, Germany’s Brexit Coordinator and Deputy Director-General for European Affairs at their Federal Foreign Office, is also pessimistic about Mrs. May producing answers in time.

“Not many are expecting very much now,” he tweeted earlier this week. “If this is so, October would then have to solve ALL problems – withdrawal, Northern Ireland, governance, and future – in one go. Odds are still unclear.”