Theresa May hopes of avoiding a chaotic Brexit face another blow from a House of Lords ambush that would stop the imposition of essential new trade rules.

The government is set to be defeated on Monday when peers rebel over ministers’ refusal to guarantee food safety, animal welfare and the power of parliament to block a free-for-all, The Independent has learned.

In an extremely rare move, the Lords is poised to vote to shelve the Trade Bill unless the government agrees to put flesh on the “skeleton” – something ministers have failed to do for 15 months.

“They need the Trade Bill for Brexit and we are extremely confident this vote will be successful, unless the government stops just saying ‘trust us’,” said a Lords source.

Under the plan, detailed scrutiny of the legislation will be abandoned until the government explains how future trade agreements will be agreed and scrutinised.

Ministers have stoked controversy about whether they would allow the import of chickens soaked in chlorine, beef fed with hormones and genetically modified crops, in the desperation for a US trade deal.

Last year, the prime minister, asked if parts of the NHS would be up “for sale”, said it was too early to judge what “requirements” the US would have in those post-Brexit talks.

Now the passage of the bill is in jeopardy with the potential derailing of an already extraordinarily tight timetable, with just 69 days until departure on 29 March.

Without the bill, the government cannot “roll over” 40 trade deals with other countries enjoyed through EU membership that will lapse if the UK leaves without a deal.

It will also be unable to sign up to the WTO’s general procurement agreement (GPA), in order to buy goods and services, presented by Brexiteers as the route to a no-deal future.

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“Certainly, it wouldn’t be possible to have the UK membership of the GPA without the legislation of the trade bill going through,” Mr Fox told MPs last month.

Explaining the move, Baroness Smith, Labour’s leader in the Lords, said: “It’s nearly 15 months since the Trade Bill was introduced to parliament.

“With just 10 weeks until Brexit day, ministers must explain urgently how trade policy will work after Brexit, including how parliament will be engaged and the role of the devolved administrations.

“We also need to know whether or not the government will agree to our call for guarantees on workers’ rights and food safeguarding standards.”

If passed with the support of independent peers, Labour’s “procedural motion” would prevent the bill’s report stage starting on 25 February until a white paper – or similar detailed proposals – have been published.

It comes after a leaked memo from Mr Fox’s department revealed that the UK will not be close to finalising replacements for the EU’s 40 existing agreements with leading global economies by Brexit day.

Compiled by civil servants at the Department for International Trade, it warned that most would be lost without the planned 21-month transition period.

Mr Fox blamed the other countries, saying: “Our side is ready. It is largely dependent on whether other countries believe that there will be no deal, and are willing to put the work into the preparations.”

A Department for International Trade spokesperson said: “The aim of the Trade Bill is to ensure the continuity of our existing trading relationships and it is not an opportunity to renegotiate the terms of the EU’s agreements.