She now appears to have given up trying to forge unity in the bitterly divided Conservative Party she has belonged to all her adult life.

Comedy of errors: meet the cast of Britain’s Brexit tragedy

The move outraged some Tories.

One member of Parliament, Henry Smith, called it a “betrayal”. Another, Marcus Fysh, accused May of “fear and vacillation”.

Meanwhile, May’s coalition partners, the Democratic Unionist party (DUP), described May’s handling of Brexit as “lamentable”.

“I think getting the support of a known Marxist is not likely to instil confidence in the Conservatives,” said Jacob Rees-Mogg, leader of the European Research Group, the most pro-Brexit faction of the party.

The prime minister said the talks with Corbyn and Labour would “try to agree a plan – that we would both stick to – to ensure that we leave the European Union and that we do so with a deal”.

Almost three years after the UK narrowly voted to leave the EU, exhausted by weeks of parliamentary shenanigans, the two leaders will have to hatch some compromise acceptable to the House of Commons and Brussels by next Tuesday at the latest.

May is due to fly to Brussels on Wednesday for a Brexit summit with the other 27 EU nations who will have to approve the deadline extension and give backing to any new proposals.

EU officials were diplomatic about May’s attempt to reach out to Corbyn who has held separate talks in Brussels.

“Even if after today, we don’t know what the end result will be, let us be patient,” tweeted the EU President Donald Tusk.

Guy Verhofstadt, the Brexit Coordinator for the European Parliament, tweeted it was “good that PM Theresa May is looking for a cross-party deal. Better late than never”.

The EU has already said it is open to extending Article 50, the legal mechanism that sets the deadline for the UK to leave the EU, but only if there is a clear purpose and plan.

If the Brexit date extends after May 22 the UK will have to participate in pan-European elections to the European Parliament the EU body that decides on the budget and elects the European Commission Executive on May 23 – 26.

What are the options and possible scenarios?

No Deal

A possible reason May extended a hand to Corbyn, after having previously said she was prepared for a cliff edge Brexit, is a leaked memo to the cabinet meeting Tuesday from Mark Sedwill, the UK’s most senior civil servant who said a “no deal” sharp divorce would trigger a recession, hammer the sterling, cause a 10 per cent rise in food prices and lead to government bailouts of masses of UK companies.

It would also, he said, disrupt national security and stability and force London to once again impose direct rule on Northern Ireland, where the majority voted to remain in the EU.

May’s deal

The agreement May negotiated with the EU seems almost dead.

Corbyn is unlikely to back a fourth attempt to gain parliamentary approval for the withdrawal agreement that maintains trade arrangements – but removes the UK’s political representation in Brussels.

The deal would keep Northern Ireland in the EU customs union to ensure free trade flows across the border to the Irish Republic, an EU member.

Northern Ireland voted to remain, but for the DUP, May’s deal smacks of an effective annexation of the province from the UK.

Customs union

Labour’s policy has been to opt for a permanent customs union with the EU for the whole of the UK as long as EU laws on environmental, food safety and worker’s protection are also maintained.

It is also the solution closest to a parliamentary majority – losing a vote last week by just three votes.

The EU is open to such an agreement that would avoid tariffs between the UK and the EU, a relief for British manufacturing, which relies heavily on imported inputs even though non-tariff barriers such as regulatory checks for plant and animal products would stay.

It might solve the Northern Ireland conundrum. Brexit hardliners reject this, because the UK would have to continue to rely on the EU for its trade deals with other countries.

Revoke Article 50

Even though May has insisted all along the results of the 2016 referendum would be respected, more than six million people have signed an online government petition to revoke Article 50 effectively cancelling Brexit.

The legal jury is still out on whether this can be done.

Second referendum

Corbyn will be under intense pressure from his MPs to make support for an agreement with May conditional on it being endorsed in a new public vote.

This could be the undoing of a compromise plan, as May has repeatedly rejected a second referendum. But Remainer Tories are also open to this idea.

On Monday, finance minister Philip Hammond, a close ally of May, said a second popular vote should be on the table.

End of May?

With Brexiteers furious about May’s compromise proposals with Labour, her own party could still do this and it could also be done with a new vote of no confidence in the prime minister and government, which would likely trigger a general election.

Any successor to May would be a hard Brexiteer who would be unable to command the support of the House of Commons.

General election

Conservative Brexiteers would likely defect to harder-right parties like the United Kingdom Independence Party or the Brexit party of UKIP’s former leader Nigel Farage.

A new centrist party has already been formed called Change UK, comprising of both Labour and Conservative MPs opposed to Brexit and the leaders of their old parties, just to confuse the mix.

Additional reporting by Bloomberg