The government is bracing itself for defeats in parliament on Brexit this week, including over its plans to take the UK out of a customs union with the EU.
Ministers have resigned themselves to the fact that the House of Lords will almost certainly pass amendments backed by Tory, Labour and Liberal Democrat peers aimed at forcing Theresa May to rethink her position.
Sources in the upper house told The Independent the only way she can realistically avoid a defeat is by making significant concessions, including one softening her approach to an EU customs union that is likely to enrage Tory Brexiteer MPs.
It comes as a new broad campaign for a “people’s vote” referendum on the final Brexit deal holds a rally in London on Sunday, following a day of action on Saturday involving thousands of activists across the country.
The prime minister’s EU (Withdrawal) Bill has already cleared its main stages in the Commons, but now faces a major challenge in the Lords where Tory peers are in a minority, even some of those have pledged to vote against the government.
The most significant amendment where the government faces defeat is that which would push it to come to an arrangement which “enables the United Kingdom to continue participating in a customs union with the European Union”.
It is backed by crossbencher Lord Kerr, who helped author Article 50, ex-Tory cabinet minister Lord Patten, Labour frontbencher Baroness Hayter and Lib Dem Baroness Ludford.
The issue is likely to come to a vote on Wednesday, with ministers yet to show any sign of budging from their position to abandon any customs union with the EU.
A government insider said: “Are we expecting a defeat? Yes, that’s about where we are.
“The government is listening on the important aspects of the bill and I think that’s what the overall tone of the debate from the crossbenchers will be – that, actually, the government is listening and taking appropriate action.
“But there was always going to be a time when this type of amendment, the customs union amendment, was going to cause a bit of a clash. We’ll just have to see how the debate goes.”
In advance of Wednesday, Brexit minister Lord Callanan has tabled a small number of government amendments in response to earlier debates, but Tory insiders have been at pains to underline how they are technical in nature and do not “compromise” on the major principles of the Bill, with Conservative right-wingers keeping a close eye on proceedings.
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But there are also a string of other opposition and rebel amendments – including on “Henry VIII powers” and protections for the Charter of Fundamental Rights – that could cause problems for the government, with more hopeful opponents of Brexit suggesting ministers may suffer up to six defeats during the bill’s report stage in the Lords.
A source in the upper chamber said: “The first rule of politics is follow the numbers.
“There has been a long run-up to this and with the numbers of peers supporting these amendments, the government has probably – unless they are going to make significant late concessions – factored in that they will endure some defeats.
“Commons whips are going to have to work out whether they take a defeat on the chin, come up with late concessions in the lower house or try and stare the Lords down with a bit of ping-pong.”
If the government is defeated then the House of Commons will have to consider the amendments that the Lords forces on the table, and while the government may overturn them in the lower house, the move could significantly delay and obstruct Theresa May’s approach to Brexit – with the legislation moving back and forth between the two houses.
Arch-Leavers such as Jacob Rees Mogg MP have called for the prime minister to flood the House of Lords with 200 new Conservative peers in order to force through her Brexit agenda.
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A government spokesperson said: “The House of Lords plays an important role in scrutinising and revising legislation and we are grateful for the contributions that have been made so far.
“Throughout the EU (Withdrawal) Bill’s passage we have demonstrated that we are listening to constructive suggestions put forward.
“This bill is about providing certainty and continuity as we leave the EU, it is not a medium to overturn the referendum.”