Downing Street has warned peers not to try and block the controversial legislation overriding parts of the Brexit Withdrawal Agreement.
The UK Internal Market Bill passed its first hurdle in the Commons on Monday, but Boris Johnson is facing a major revolt of around 20 senior Conservatives over an amendment to the bill, which could break international law.
The legislation would give ministers sweeping new powers to ensure unfettered access between Northern Ireland and the rest of the UK.
Some peers have warned that the bill will not get through the upper chamber in its current form.
A No 10 spokesman responded, saying ministers believed the Salisbury Convention – which states the House of Lords should not vote down legislation to implement Government manifesto commitments – should apply.
“We would expect the Lords to abide by the Salisbury Convention,” the spokesman said.
“Guaranteeing the full economic benefit of leaving the EU to all parts of the United Kingdom and ensuring Northern Ireland’s businesses and producers enjoy unfettered access to the rest of the UK were clear Conservative manifesto commitments which this legislation delivers.”
She contradicted Cabinet colleague Brandon Lewis by denying his dramatic Commons admission that the Government is ready to break international law in a “very specific and limited way”.
Speaking after a major rebellion by around 20 senior Conservatives against the new Internal Market Bill, the Home Secretary appeared to signal a climbdown by declaring: “We are absolutely not doing that.”