The Democratic Unionist Party (DUP) leader has brought the Irish Sea border into the centre of Northern Ireland’s election campaign.

That internal trade border exists as a result of the UK’s 2019 Brexit deal with the EU.

It has been modified, simplified and repackaged in subsequent deals but is still there.

As he was confirmed as leader this week Gavin Robinson told his party: “We will continue to fight to fully restore Northern Ireland’s place within the United Kingdom, including removing the application of EU law in our country and the internal Irish Sea Border it creates.”

This is a change in rhetoric from February when the DUP decided to return to Stormont after a two year boycott in protest at the sea border.

The then DUP leader, Sir Jeffrey Donaldson, said a UK-EU deal and a side-deal between the government and the DUP “takes away the border between Northern Ireland and Great Britain and that is something very important”.

There was nuance if you looked for it, with Sir Jeffrey acknowledging the deal was not perfect, but the overall DUP message was effectively: “Sea border gone. Back to Stormont. Let’s move on.”

Mr Robinson has decided that position is not sustainable in an election campaign where the deal will be challenged and unpicked by unionist rivals.

He conceded the deal had been oversold and there should have been more “cautious realism” at the time.

Mr Robinson has been moving to this position since he became interim DUP leader in March.

He gave an interview to the BBC’s Talkback programme, which he described as “boringly detailed”, outlining the nuances of what had been agreed.

That looked like a move towards a more defensible position in the face of criticism of the deal from dissenting voices, some of which are inside his own party.

“It’s an electoral tightrope,” says Prof Jon Tonge, professor of politics at Liverpool University.

“The electorate might reward you for your honesty or they might feel a bit aggrieved.”

He says polling suggests that the bulk of DUP supporters were content with the return to Stormont but a minority were not and it is that smaller group which is being targeted with the new approach.

“It’s about the part of the DUP base which isn’t happy with what has happened. That will really determine the fate of the DUP in a number of constituencies,” he says.

The DUP cannot by itself change the operation of the sea border or the application of EU law in Northern Ireland.

There will be a democratic consent vote at Stormont later in 2024 on ending or continuing the current arrangements.

That is a simple majority vote meaning non-unionist parties have the numbers to continue with the current arrangements.

There are also two “democratic consent mechanisms” at Stormont which gives the assembly the power to recommend the blocking of new or updated EU rules from applying in NI.

However it is ultimately for the UK government to decide.

It would be open to a new UK government to ask the EU to reopen negotiations on the Northern Ireland Brexit deal but the Queens University expert Prof David Phinnemore says that is very unlikely.

“I can’t see there being any push to change the Windsor Framework,” he says, referring to the current Northern Ireland deal.

“The negotiating space there with the EU has been exhausted. If there’s going to be any change it’s going to come through the wider EU-UK relationship.”

One of Labour’s clearest and most consistent polices is that it will seek a new agreement for agri-food products traded between the UK and EU with the aim to “eliminate most border checks created by the Tory Brexit deal”.

Such a deal could at a stroke sweep away the most obvious physical impacts of the Irish Sea border and end some of the most onerous paperwork.

In simple terms if a deal ends checks on goods moving from Calais to Dover then checks will also end from Cairnryan to Belfast.

Agrifood deals from the EU fall into two broad categories: New Zealand-style or Swiss-style.

A Swiss-style deal is the more dramatic. Since 2009, there have been no regulatory border controls for trade in agrifood products between Switzerland and the EU.

But the Swiss only have this deal because they agreed to follow EU rules almost to the letter, without much say in setting those rules.

Switzerland is obliged to modify its laws in response to changes in EU legislation, what is known as dynamic alignment.

When BBC NI asked Keir Starmer about this last year he said: “I’m not interested in a deal that puts the UK in a position of being a rule taker. Our rules must be made in Westminster, according to the national interest of the UK as a whole.”

Mujtaba Rahman, a managing director at the Eurasia Group consultancy and long-time Brexit watcher, says an agrifood deal will nonetheless be high on the agenda.

“The likely priority of a Starmer government will be renewed foreign and security policy cooperation with the EU, while simultaneously addressing a number of irritants that flow from the Trade and Cooperation Agreement (TCA).

“A deal to reduce friction on agricultural goods is likely to be one of those priorities.”

The general election is to elect Members of Parliament – or MPs – to the House of Commons.

The UK is divided into 650 areas, called constituencies, and each of these elects one MP to represent local residents at Westminster.

Most candidates represent a political party, but some stand as independents.

Northern Ireland will elect 18 MPs.

The Electoral Office has set up an online service to help people check if they are registered, external to vote in Northern Ireland.

To register to vote in Northern Ireland, you must be aged 16 or over, however you must be over 18 to be included in the UK parliamentary register.

Registered voters who are unable to attend polling stations in person can apply for a postal or proxy vote.