The campaigner who forced Theresa May to ask Parliament’s permission to trigger Article 50 has demanded the House of Lords show “backbone” and push the Government into concessions on Brexit.

Speaking exclusively to The Independent, Gina Miller said those debating Ms May’s Article 50 Bill this week must take the lead because the House of Commons had shown “cowardice” in failing to win any compromise.

Peers may use sittings on Monday and Wednesday to push for votes on key amendments, including ones demanding a guarantee for EU citizens’ rights and for a vote on the final deal Ms May secures from the EU on Brexit.

But the upper chamber is under immense pressure to wave the Bill through unchanged, ratcheted up by Ms May’s decision to personally attend the Lords last week and monitor them discussing her legislation.

Ms Miller said the Prime Minister was clearly trying to “bully” the Lords and even compared her to the tyrannical character Miss Trunchbull, from Roald Dahl’s children’s novel Matilda, who browbeats children into submission.

The philanthropist was the lead voice among a group of campaigners who prevented Ms May from unilaterally launching the countdown to Brexit using Royal Prerogative powers, arguing at the Supreme Court that Parliament must vote on the issue.

But Ms Miller told The Independent that after she and her team won the right for Parliament to be consulted, she now fears the upper House will bow to media pressure and pass the Bill unamended.

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

She said: “I think it’s absurd this idea that the Lords should just get on with it and not have a proper debate. After we fought so hard to put the Commons back at the centre of the debate, all the Commons did was rubber stamp the Bill – which was cowardice.

“I am hoping the Lords actually do what they should be doing constitutionally – exercising their parliamentary sovereignty, being independent, scrutinising the Government and looking to put in amendments.”

Ms Miller is no stranger to media pressure, having received a torrent of abuse for leading the charge against the Government in the Supreme Court case on Brexit.

She said peers are now being “picked off” and “bullied” by elements of the media into abandoning their constitutional duty to scrutinise Ms May’s Bill, adding that the Prime Minister has also sought to intimidate the upper House.

Theresa May sits in House of Lords to hear Brexit debate

Discussing Ms May’s appearance in the Lords as it debated the matter, Ms Miller said: “She was sitting there like Miss Trunchbull from Matilda, it was absolutely shocking.

“The only conclusion I can come to is that she was trying to bully them. Why else would you be there?”

In Dahl’s classic story, sadistic head-teacher Miss Trunchbull, whose motto is “use the rod, beat the child”, eventually comes a cropper when she pushes the wrong schoolgirl too far.

Ms Miller is particularly keen to see an amendment passed in the Lords which forces Ms May into guaranteeing that Parliament has a meaningful vote on the final deal she secures after talks in Europe.

That does not mean simply a choice between leaving the EU on Ms May’s terms or leaving without a new trade deal with the EU, as Ms Miller explained: “A choice between shooting yourself in the foot with an arrow or a pistol is not a choice.”

Instead she wants “all the options” to be on the table. A drive in the Commons to see the promise of a vote on the final deal written into the Bill was dropped, after the Government gave a verbal assurance to MPs that a vote would happen.

But Ms Miller said a “political promise is worth nothing”, adding: “They should be amending it. These people who are standing up and constantly claiming that amendments are going against the will of the people are wrong, it’s got nothing to do with that.

“This is about triggering Article 50, going forward and putting in some safety valve if it’s needed in the future… we have to an opportunity where Parliament is able to vote on all options – that amendment is absolutely crucial.”

Peter Mandelson: Peers should not 'throw in the towel’ over Brexit

Last week Labour peer Peter Mandelson wrote exclusively for The Independent also demanding the British people are given the chance to have their say on Ms May's Brexit deal, through a vote in Parliament or even a referendum.

Peers have proposed a string of amendments to Ms May’s bill, some of which have cross-party support. Whether they are pushed to a vote in the coming week will be down to how reasonable the Government is at taking on board peers’ concerns.

It may be that ministers go away promising to rewrite the bill to account for some of the concerns raised, thus putting off the threat of a vote and defeat in the Lords to a later stage in the process.

Labour insiders believe that the Government may be ready to try and compromise on the issue of vote on Ms May’s final deal and so the issue might avoid a vote this week.

If a vote does occur, it is most likely to be on the amendment to guarantee the rights of EU citizens living in the UK, which enjoys support from every part of the Lords.

In the instance that the Lords does vote to amend the Bill, those changes would then have to go back to the Commons for approval.