The Great Repeal Bill – which does the opposite of what it says – could be the Brexit act that finishes off Theresa May

There are between 20 and 30 pro-European Conservatives; only seven need to vote with all the opposition parties to defeat the Government’s ‘majority’

Theresa May’s appeal for opposition parties to cooperate with her minority government didn’t just produce the inevitable raspberry from Labour. It also went down very badly with Conservative MPs, who gave the Prime Minister another black mark just when she hoped she was stabilising her position.

“She only advertised her weakness,” one grumbled. Only the most sycophantic and ambitious Tories went on the airwaves to defend May’s plea. Perhaps she hoped for a brownie point from voters fed up with yaboo politics.

Although Jeremy Corbyn is a more tribal figure than some of his predecessors, I suspect even Tony Blair would have reacted in the same way – offering to send Labour’s election manifesto to the PM.

May’s overnight conversion from control freak dictator to consensual leader will fool no one; only two months ago, her allies were talking about a landslide that would crush Labour and keep it out of power for a generation.

May is limping towards the finishing line of next week’s parliamentary summer break, when her Tory critics will have to discuss her shelf life by phone rather than in dark Commons corners. Although many Tory MPs want May to see the Brexit negotiations through to their close in 2019, it is only because they fear a change of leader would fuel demands for another general election.

The PM’s fragility will be underlined on Thursday with the publication of the Repeal Bill: the first of eight pieces of Brexit legislation. The mammoth Bill would have been complicated enough even if May had won her landslide. Now opposition parties and Tory pro-Europeans will be able to wage parliamentary guerrilla war against the Government – not exactly the cross-party co-operation May had in mind.

The Government is so nervous about rebellions that it will delay any debate on the Bill until October. There are between 20 and 30 pro-European Conservatives; only seven need to vote with all the opposition parties to muster 320 votes and defeat the 319 from the remaining Tory MPs and 10 Democratic Unionists.

The Bill really does the opposite of what it says on the tin. While it will abolish the 1972 European Communities Act which took us into the EU, it will transpose 44 years of EU legislation, including 19,000 regulations, directives and other rules, into UK law. (They are still coming: another 1,200 are expected before we leave in 2019). This would give ministers time to decide which EU rules to keep, which Whitehall officials believe could take 10 years.

The early skirmishes will likely be about the streamlined procedure proposed by ministers to make this huge task manageable. They want to assume so-called “Henry VIII powers,” named after the monarch who ruled by proclamation, allowing some decisions on EU rules to be taken without the full parliamentary scrutiny given to Bills.

Between 800 and 1,000 “statutory instruments” will be needed. Ministers insist they will use secondary legislation, which can be passed without a Commons and Lords vote, only for technical changes – for example, replacing an EU regulatory agency with a UK one.

But nothing excites MPs and peers more than their own powers – and this time they are right to be worked up. The constitutional brigade in the Lords will rightly lead demands for safeguards so that ministers cannot by decree dilute EU standards on issues such as workers’ and consumer rights and environmental standards. Ministers will almost certainly have to give some ground.

They have a presentational problem: Brexit is supposed to be about the UK Parliament “taking back control” of laws made in Brussels. Tricky.

MPs and peers regard the Repeal Bill as a “Christmas tree”: parliamentary language for a measure on which they can hang virtually anything they want. So pro-Europeans might try to table amendments saying the UK should maintain the benefits of the single market and customs union.

It is not yet clear whether such amendments would be allowed, but where there’s a will, MPs and peers normally find a way.

They will try to use the Bill to soften May’s dogmatic aversion to the European Court of Justice (ECJ), which risks preventing sensible cooperation with the EU on issues such as pharmaceuticals and atomic energy. There will also be a row about the Government’s proposal not to write the EU’s charter of fundamental rights into UK law.

May will argue that Parliament cannot dictate the negotiations with the EU, which will be in full swing as it debates the Bill. But May’s lack of a majority will make it harder to close down debate.

The Bill will eventually become law – in order to avoid a “cliff edge” of no regulations in March 2019. The question is not whether it will be amended, but how.

We have already seen May back down to head off Commons defeats by funding abortions in England for women in Northern Ireland, and by setting up an inquiry into the contaminated blood scandal in the NHS. A spectacular defeat on the Repeal Bill could even be the final straw which persuades Tory MPs to force May out.

As one senior Tory put it: "She will go after an unexpected event. The Repeal Bill could provide it.”