Tory grandee Michael Heseltine has signalled he is ready to defy Theresa May over Brexit and will fight to change her plan to trigger Article 50 in the House of Lords.

The Conservative peer said he was intent on ensuring that people have a chance to change their minds, raising the prospect of a second referendum should public opinion demand it.

Tomorrow peers will begin debating Ms May’s bill to launch Brexit talks, with discussions eventually moving on to a cross-party plan to force the Government to guarantee Parliament a meaningful vote on the final deal the Prime Minister secures with the EU.

Gina Miller, whose Supreme Court action forced Ms May to give Parliament a vote on triggering Article 50, called on the Lords to show “backbone” in challenging Ms May’s Brexit plan.

Lord Heseltine’s comments also follow similar demands from Labour peer Lord Mandelson who made a call in The Independent for people be given the chance to have their say on Ms May’s Brexit deal, through a vote in Parliament or even another referendum.

Writing in The Mail On Sunday, Lord Heseltine said: “I have never known a future populated by such uncertainty but my preoccupation is to ensure that if public opinion changes then Parliament has the means to reflect that, whether by election, referendum or rethink.”

He added Labour, Lib Dem and rebellious Tory colleagues also want a change to the Brexit bill that will mean MPs and peers have ultimate authority over how the UK leaves.

The Conservative peer went on: “In the end the outcome of Brexit will have to be confirmed by Parliament. It will also have to pass in 27 national European parliaments, several sub-national parliaments and the European Parliament.

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“It was perhaps unwise for our Government to suppose that our Parliament should be excluded where all others were included. Very sensibly, after the Supreme Court interpreted the law, that position was reversed and Parliament was restored to its rightful constitutional role as the ultimate authority.

“I will vote in the House of Lords to ensure that position is legally intact. This is not a confrontation with the Government which has already made such a commitment.”

A Labour Lords source said the party “would be likely to win handsomely” if the issue came to a vote, though ministers may seek to avoid testing the theory this week by promising to make concessions to delay it.

Supreme Court Brexit Challenge Show all 13 1 /13 Supreme Court Brexit Challenge Supreme Court Brexit Challenge People wait to enter the public gallery outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge Gina Miller, co-founder of investment fund SCM Private arrives at the Supreme court in London on the first day of a four-day hearing Getty Supreme Court Brexit Challenge A man waves the EU flag in front of the Supreme Court Getty Supreme Court Brexit Challenge Satirical artist Kaya Mar poses with two of his paintings in front of the Supreme Court Getty Supreme Court Brexit Challenge Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin. The eleven Supreme Court Justices will hear the government's appeal, following the High Court's recent decision that only Parliament can trigger Article 50 Getty Supreme Court Brexit Challenge The eleven Supreme Court Justices will hear the government's appeal, following the High Court's recent decision that only Parliament can trigger Article 50 Getty Supreme Court Brexit Challenge Businesswoman Gina Miller arrives at the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin Getty Supreme Court Brexit Challenge Attorney General Jeremy Wright arrives at the Supreme Court in London EPA Supreme Court Brexit Challenge Protesters outside the Supreme Court in London, where the Government is appealing against a ruling that the Prime Minister must seek MPs' approval to trigger the process of taking Britain out of the European Union PA wire Supreme Court Brexit Challenge A protesters wearing a judge's wigs and robes stands outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge A protester holds up a placard outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court Getty Supreme Court Brexit Challenge A man waiting to enter the public gallery waves a European Union flag outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters

Any vote that does occur will most likely be on the amendment to guarantee the rights of EU citizens living in the UK, which has wide support in the Lords.

Should a vote be made to amend the bill in the upper chamber, those changes would then have to go back to the Commons for approval.