"Nothing is off the table" when it comes to reassuring MPs over the Northern Ireland backstop, Downing Street sources say.

This could include reopening the EU withdrawal agreement, even though that comes with risk, the sources say.

Theresa May is understood to be pushing the EU for flexibility on the backstop.

This is the clause in the prime minister's EU withdrawal agreement that is meant to prevent the return of border checks in Northern Ireland.

It would see the UK aligned with EU customs rules until a future trade deal is agreed that does not include a physical border between the EU and the UK on the island of Ireland.

The backstop is meant to be a temporary measure but the UK can't leave it without the EU's say-so, under the terms of the withdrawal agreement.

Many MPs fear this will mean the UK will end up indefinitely tied to the EU with no say over its rules - and that is why they are planning to vote against the withdrawal agreement on Tuesday.

Those campaigning for another EU referendum have, meanwhile, been given a boost by the European Court of Justice (ECJ), which has ruled that the UK can cancel Brexit without the permission of the other 27 EU members.

Former foreign secretary Dame Margaret Beckett, who is campaigning for another referendum, said: "This is confirmation that it is still up to us to decide whether we want to keep the existing deal we've got in the EU rather than accept a bad deal negotiated by the government."

But Environment Secretary Michael Gove said the ruling does not alter the government's intention to leave the EU in March 2019.

He told BBC Radio 4's Today programme: "We voted very clearly - 17.4 million people sent a clear message that we wanted to leave the European Union and that means also leaving the jurisdiction of the European Court of Justice.

"So, this case is all very well but it doesn't alter either the referendum vote or the clear intention of the government to make sure that we leave on 29 March."

He rejected newspaper reports that Tuesday's Commons vote will be cancelled to prevent the prime minister suffering a defeat of historic proportions that could end her premiership.

Mrs May has previously insisted there can be no deal with the EU without the backstop - and it would be impossible to change the terms of the withdrawal agreement.

She has repeatedly warned her own MPs that a rejection of her deal could lead to a general election - or possibly "no Brexit" at all.

That has so far failed to convince dozens of Tory MPs who are planning to join Labour, the Liberal Democrats, the DUP and the SNP in voting against it.

So, in a change of tone, Downing Street is now saying the withdrawal agreement could be tweaked to reflect concerns about the backstop.