Theresa May is preparing to counter a new rebellion tonight from her own MPs over her Brexit plans.

Eurosceptic Tory MPs will vote for amendments which would block her so-called Chequers deal.

While the amendments are unlikely to pass, they will give the PM a clear indication of how many MPs are prepared to torpedo her proposals.

Arch-Remainer Justine Greening — an ex-Cabinet minister — gives May a further headache by calling for a second Brexit referendum.

The prime minister suffered another government resignation on Sunday as fears of a vote of no confidence in her leadership grow.

LONDON — Theresa May is braced for a major rebellion on two fronts in the Commons this evening as Eurosceptics and Remainers in her own party threaten to kill off her Brexit plans.

MPs are set to vote on several amendments to the customs bill — a crucial piece of Brexit legislation — which have been tabled by the European Research Group, a hardline group of Eurosceptic Tory MPs.

Their plan is simple: to kill off Theresa May's so-called Chequers plan, the Brexit compromise which has gone down badly with both Leavers and Remainers alike.

The plans, published in a White Paper last week, would see May ask Brussels for a "common rulebook" between the UK and EU and maintain close customs ties. But Eurosceptic Conservative MPs say it's a compromise too far and Remain-supporters suggest it would be the worst of all worlds.

The fresh rebellion comes as Conservative whips seek to persuade MPs unhappy with the prime minister to step back from forcing a leadership contest against her.

Under Conservative party rules, a contest can be forced if 48 or more Tory MPs submit a letter to the chair of the 1922 committee requesting a vote of no confidence in her.

May has suffered a string of resignations from Cabinet members and ministerial aides over the past week.

The crunch vote

Tonight's amendments would make May's plan unworkable by blocking specific proposals on customs and the Irish border.

Tory MP Steve Baker, who resigned a ministerial post last week along with David Davis and Boris Johnson, is reportedly co-ordinating a 100-strong group of Brexiteers through a WhatsApp group, though fewer than half of that number appears likely to vote against the prime minister.

And while the amendments are unlikely to pass — because Labour will not support them — it will give May a clear sense of the scale of the rebellion facing Theresa May from her own back-benches by indicating how many of her MPs are ready to vote against her Chequers proposals.

That, in turn, will prove the PM with a clear sense of how many MPs would be willing to vote against a final Brexit agreement this Autumn — so it's a big deal.

Make-or-break: The third reading

UK Prime Minister Theresa May BBC News The more pressing issue for the government is the third reading of the customs bill at around 10 p.m. tonight, because it remains unclear whether the legislation will actually pass through the Commons.

Labour MPs will be whipped to vote against the bill as it is deemed to fail some of the party's "six tests" for an acceptable Brexit. That means May will rely on her slim majority in parliament, which is propped up by DUP votes.

The government is reportedly ready to offer concessions on several of the amendments in order to head off rebels, but the scale of the retreat will not become clear until later today.

It is absolutely crucial for May that the Bill passes because failure could mean another week of terrible headlines and personal attacks as Tory MPs return from their weekends reporting furious constituents who believe May's Brexit plans represent a betrayal of the project.

Remainer "rebels" co-ordinate an attack

That's not all. Theresa May is also under attack from the Remain wing of her bitterly divided party, with former Cabinet Minister Justine Greening launching a scathing attack on her Chequers plan and calling for a second Brexit referendum.

The Times reports that Dominic Grieve and Amber Rudd — two other senior Tory MPs — are set to join Greening in the coming days in what is likely to have been a co-ordinated Remainer manoeuvre. Greening's intervention follows newspaper op-eds from arch-Remainers including Nick Clegg, Peter Mandelson, and Tony Blair.

The Remainers represent another headache for May, although a much smaller one than the Eurosceptics. While they will not vote for the Brexiteers amendments this evening, they could vote against the Bill itself at the third reading to pile more pressure on May and force her into a retreat from the Chequers plans.

That appears unlikely, however. The so-called Remain-supporting "rebels" have threatened to vote against the government before only to back down with only the vaguest concessions. They are particularly wary of inflicting a defeat on May as she appears most vulnerable to the Brexit-supporting wing of the party.

The working Tory Remainer strategy appears to be to threaten to vote against the government to force minor concessions but ultimately to fall in line at the last minute for fear that toppling May would lead to something worse.