The PM has returned from EU talks with three new backstop assurances, and the attorney general has given his verdict. What happens next?

Theresa May has come back from Strasbourg with three new assurances on the backstop which she hopes will convince Conservative MPs and the DUP to back her Brexit deal in the vote on Tuesday night. But what is the deal and what will it change?

Have any changes actually have been made?

There are three component parts of the new assurances for MPs, but none actually reopen the withdrawal agreement or remove the backstop mechanism.

The president of the European commission, Jean-Claude Juncker, described the latest text as something that “complements” the existing 585-page withdrawal agreement “without reopening it”. Since that withdrawal agreement was agreed between EU leaders and May in November, the EU has insisted it would not change the Irish backstop.

What are the three assurances?

The first is a joint interpretative instrument, designed to give legally binding assurances to the letter written by Juncker and Donald Tusk, the European council president, , in January that the backstop cannot be a permanent solution to the Northern Ireland border issue. The document is intended to have equal legal weight to the withdrawal agreement itself.

The second is a joint statement on the future trade relationship which says both sides will pursue “alternative arrangements” to the backstop over the next 20 months in good faith.

Thirdly, the UK has issued its own unilateral declaration, asserting that it will apply to the independent arbitration panel to dismantle the backstop provisions if the government believes the EU is not making efforts to end the arrangement. The EU has not formally objected to this document, which UK ministers have said means it has legal weight.

What does the UK government say?

“MPs were clear that legal changes were needed to the backstop,” May said in Strasbourg. “Today we have secured legal changes.”

Tory Brexiter support for May deal to hinge on legal advice Read more

Michael Gove, the environment secretary, said the EU had “made clear that the backstop is intended to be temporary – that is clear, it is in black and white and it’s a legally binding declaration”.

However, by the UK government’s own admission in the motion laid before parliament, the new assurances “reduce the risk the UK could be held in the backstop indefinitely” but they do not eliminate it.

Has this changed the legal advice on the backstop?

Both May and Gove appeared convinced that it would. Brexiters in the Conservative party have said they will be guided by the advice of the attorney general, Geoffrey Cox, and the reaction of DUP MPs.

Cox’s previous legal advice said the backstop “would endure indefinitely until a superseding agreement takes its place in whole or in part”.

In revised advice published on Tuesday morning, Cox said the risk of the UK being stuck in the backstop had “reduced”, but concluded: “The legal risk remains unchanged that … the United Kingdom would have, at least while the fundamental circumstances remained the same, no internationally lawful means of exiting the protocol’s arrangements, save by agreement.”

The shadow Brexit secretary, Keir Starmer, a former director of public prosecutions, had already released his own legal assessment on Tuesday morning. Starmer’s advice said: “The withdrawal agreement does not include a mechanism for unilateral exit from – or termination of – the backstop (or any other part of the agreement) even where bad faith is made out.

“Turning the content of the 14 January letter from Donald Tusk and Jean-Claude Juncker into a joint interpretative declaration does not change that. Nor in my view does anything else agreed last night.”

What else will Brexiters use to assess the deal?

The European Research Group of Tory Brexiters has said a group of eight lawyers, seven of them MPs, will scrutinise and pass judgment on Cox’s final analysis of the offer. The group met at 9am on Tuesday and is expected to decide whether to recommend accepting the assurances in the afternoon.

The seven MPs include Nigel Dodds , the deputy leader of the Democratic Unionist party (DUP), whose opinion carries weight with Eurosceptic Conservatives, as well as the former Brexit secretary Dominic Raab, the ex-ministers David Jones and Suella Braverman, the veteran Brexiter Bill Cash and the backbenchers Michael Tomlinson and Robert Courts. They are joined by Martin Howe QC, the chair of the pro-leave group Lawyers for Britain.

Will May’s deal pass with these new assurances?

The verdict of the DUP will be the key for the vast majority of Tory MPs. Jacob Rees-Mogg, the chair of the ERG, said his decision would be influenced most by the verdict of Dodds and the DUP, which is also likely to guide the final decision of the so-called “star chamber” of Eurosceptic lawyer MPs.

Will the votes of Tory Brexiters and the DUP be enough?

May will still probably face opposition from some remainers in her party as well as a hardcore faction of Brexiters. The prime minister is still likely to need the backing of a significant number of Labour MPs, and many have signalled they do want to find a route to vote for her deal.

However, two key issues are holding back many Labour votes. Firstly, MPs feel compromised and bruised by how badly May’s promises on workers rights went down with the unions and the think the size of the sums offered in her “left-behind towns” fund were insubstantial.

Secondly, MPs who would back the deal as a way to avoid no deal have an option to delay their “high noon” because May has promised a vote on delaying article 50. Many may decide not to jump now because they cannot then say to angry party members it was this or no deal.