Sir Oliver Letwin has joined a group of senior Conservative Party figures calling on Theresa May to abandon the UK government's appeal against a high court ruling on the triggering of Article 50. Pursuing the appeal, he said, could jeopardise the entire process of the UK leaving the European Union.

The government faced a legal challenge last month after it said it would enact Article 50 – the clause of the Lisbon Treaty that triggers the departure of a member state from the EU – without first asking Members of Parliament to vote on the process. After the High Court ruled in favour of the challenge, made by Gina Miller, the government said it would appeal against that decision.

Speaking to the BBC's Today Programme, Sir Oliver said of the appeal, which is due to be heard between 5-8 December at the Supreme Court, there were advantages to following the legislative process.

He said: "One of the advantages of the government bringing a fast and tightly timetabled and constrained bill to the House of Commons and the House of Lords and passing it through, and having an act of parliament that beyond any doubt gives the government the ability to trigger Article 50 without any constraints on its negotiating power now, rather than appealing to the Supreme Court, is that it avoids any risk of the Supreme Court deciding to accord the devolved administrations some rights, or even some veto powers, over the triggering of article 50."

The comments follow an announcement by the Supreme Court on Friday (November 18) that it would permit the Scottish and Welsh devolved governments to intervene in the court case. Scotland voted in favour of remaining a member of the EU in the June referendum and it's First Minister, Nicola Sturgeon, has been outspoken about her intention to secure the best deal for Scotland – which could mean attempting to block the triggering of Article 50.

Sir Oliver, who campaigned to remain a member of the EU, joined a handful of other senior figures in the Conservative Party, including former Attorney General Dominic Grieve and Sir Edward Garnier, a former solicitor. Both publicly criticised the government for pursuing an appeal against the High Court ruling, as well as for failing to protect the judges who presided over the ruling following a public backlash.

Following some media reports in the wake of the ruling, referring to the High Court judges as "enemies of the people," Grieve said: "I was horrified at the newspaper coverage which reminded me of Robert Mugabe's Zimbabwe.

"The judges did exactly what was asked of them. They highlighted that our constitution does not allow you to overturn the statute of law by decree, which is so well established in this country." He added that there was little point of continuing with the case when an act of Parliament was unlikely to be opposed.

Earlier this month, Conservative MP Stephen Phillips – who was in favour of Brexit – resigned citing "irreconcilable differences" over the handling of the process to withdraw from the EU.

He said: "Not giving parliament the chance, before Article 50 is invoked, to say where it thinks these negotiations should end up is, at its core, undemocratic, unconstitutional and likely to exacerbate the divisions in our society to which the referendum gave rise.

"It also ignores the views of nearly half the people who voted in the referendum, who were perfectly content with our place in the EU."

Gina Miller
Gina Miller speaks to the press after the High Court ruled that the prime minister cannot trigger Brexit without the approval of MPs Niklas Halle'n/ AFP