Explainer-What is the Northern Ireland protocol?

LONDON (Reuters) - Britain and the European Union are working to agree post-Brexit trading arrangements for Northern Ireland.

Below are details on the talks and hurdles to be overcome:

WHY NORTHERN IRELAND?

Northern Ireland is a British-ruled province and part of the United Kingdom that shares a long border with Ireland, a member of the European Union.

When Britain left the European Union, what to do about trade over the open border was one of the most difficult parts of the Brexit negotiations.

WHAT IS THE NORTHERN IRELAND PROTOCOL?

To avoid the need for a hard border with Ireland and to prevent goods flowing unchecked into the EU's single market, former prime minister Boris Johnson agreed to effectively leave Northern Ireland within the EU's single market for goods. This means the province has to follow the bloc's rules in relation to those movements.

Northern Ireland also remains part of the UK's customs territory, effectively creating a customs border in the sea between Britain and Northern Ireland. Pro-British communities in the province say this erodes their place within the United Kingdom.

The Democratic Unionist Party (DUP), Northern Ireland's biggest unionist party, also says the province should not have to follow EU laws without having a say.

London says the bureaucracy - checks and paperwork for the trade of some goods - created by the protocol is threatening the 1998 peace agreement that mostly ended three decades of sectarian violence in the province.

While opinion polls have consistently shown a majority of Northern Irish voters - who opposed Brexit - favour the idea of the protocol, the province's assembly and power-sharing government have not sat for a year due to unionist opposition.

Technical talks resumed in October for the first time in seven months, shortly after Rishi Sunak was appointed Britain's third prime minister in as many months.

WHAT ARE THE MAIN ISSUES?

Customs

In January, Britain and the EU agreed a way forward on sharing live data on trade with Northern Ireland, ushering in a likely agreement on customs that would involve green lanes for goods bound only for Northern Ireland and red lanes for products heading into Ireland.

European Court of Justice

Officials have declined to comment on how they will ease the concerns of the DUP and some pro-Brexit members of Britain's ruling Conservative Party over the role of the European Court of Justice, or rather the application of EU law in a British-governed province.

The DUP says any new arrangement "must give the people of Northern Ireland a say in the making of the laws which govern them".

The protocol specifies those EU regulations and directives with which Northern Ireland must remain aligned, and means new EU acts may be added to those that apply in Northern Ireland.

A possible fix is for the EU and Britain to present the role of the ECJ differently. London would play up the role of Northern Irish judges, while the ECJ will be the ultimate arbiter of disputes about EU law in the province. This has drawn criticism from Brexit-supporting Conservatives, who say it does not solve the problem of Northern Ireland having to follow EU law.

OPPOSITION OR SUPPORT?

The British government has been at pains to keep the negotiations as private as possible, but this has fuelled speculation over how far the two sides have moved to overcome some of the issues.

At a meeting with Sunak this month, the DUP tentatively welcomed progress in the talks but reiterated its seven tests to be able to approve any deal. Some DUP members have said they will not support any deal which fails to hand Northern Ireland the power to reject EU laws.

Pro-Brexit Conservatives, who are part of the so-called European Research Group (ERG), have said they will support the stance of the DUP, while raising concerns over the continued role of EU law in Northern Ireland and over the government's reported plan to drop the Northern Ireland Protocol Bill.

The Northern Ireland Protocol bill, if passed by parliament, would give the British government the power to unilaterally decide to all but renege on the agreement.

Some ERG members fear Sunak is negotiating little more than a fudge to the existing protocol.

Sunak, who has been meeting with the ERG to ease their fears, has repeatedly said he wants to safeguard Northern Ireland's place in the United Kingdom and find solutions to practical problems.

(Reporting by Elizabeth Piper in London, Amanda Ferguson in Belfast and Padraic Halpin in Dublin; Editing by Janet Lawrence and Christina Fincher)