Theresa May turned up in the House of Lords to pile pressure on peers not to defy her, as debate got underway on the Brexit Bill.

The Prime Minister took the highly unusual step of sitting on the steps of the royal throne from where she could watch members of the unelected upper chamber closely.

One veteran said she had never previously known a Prime Minister to appear in the Lords – illustrating the historic nature of the Bill and the high stakes.

Earlier, Ms May made clear she expected peers to follow the lead of the House of Commons, which did not change or delay the landmark legislation.

Speaking on a visit to Stoke ahead of this week’s by-election there, the Prime Minister said: “I hope that the House of Lords will pay attention to that.

"Properly, there will be debate and scrutiny in the House of Lords, but I don’t want to see anybody holding up what the British people want, what the people of Stoke-on-Trent voted for last year, which is for us to deliver Brexit, to leave the European Union.”

Ms May was allowed, with Commons Leader David Lidington, to sit on the throne's steps in the Lords as a member of the Privy Council.

Baroness Royall, the former Labour leader in the Lords tweeted: “Theresa May on the steps of the throne to listen to the beginning of the Article 50 debate. Amazing. Never known the PM to be present.”

However, the Government lacks a majority in the Lords, with 252 Conservatives among the 805 peers - giving the opposition and independent crossbenchers a chance to inflict defeats.

Labour and Liberal Democrat peers have said they are confident of passing an amendment to immediately guarantee the rights of the 3m EU citizens in the UK after Brexit.

They may also succeed in an attempt to ensure Parliament is given a decisive vote on any final deal that the Prime Minister secures – and, crucially, if she fails to agree one.

Opening the marathon debate, Lords leader Baroness Evans echoed the Prime Minister by insisting the Government had a "strong mandate" from the people and elected MPs to trigger Article 50.

"This Bill is not the place to try and shape the terms of our exit, restrict the Government's hand before in enters into complex negotiations or attempt to re-run the referendum," she warned.

No fewer than 190 peers have put themselves forward to speak in the Article 50 Bill – 80 today and 110 tomorrow – in sittings expected to last until midnight on both days.

However, there are not likely to be any votes on the most explosive amendments until next week.