By Lewis Denison, ITV News Westminster Producer
The Northern Ireland Protocol is back in the news again, with another prime minister seeking to resolve one of the biggest sticking points on Brexit.
Rishi Sunak has met political leaders in Northern Ireland in a bid to restore powersharing there amid a longstanding disagreement on the protocol which has resulted in unionists blocking the formation of government.
The Democratic Unionist Party and UK government wants to change the Northern Ireland Protocol but republican party Sinn Fein, which has a majority, and the European Union wants it to stay the same.
What is the Northern Ireland Protocol?
It's a trading arrangement agreed between former prime minister Boris Johnson and the EU, which was designed to ensure harmony between bloc member the Republic of Ireland and its departing northern neighbour.
The UK government wanted to allow free flowing trade on the Island of Ireland as well as between Great Britain and Northern Ireland - but the EU said that could result in some UK goods entering the European market without being subject to their rules and regulations.
The EU has strict rules food rules and requires checks on goods like eggs and milk when they arrive from other countries.
The importance of getting the deal right was underpinned by the Good Friday Agreement (GFA), which brought peace to the region in 1998 under the condition that Northern Ireland should remain an equal part of the UK unless a majority agreed otherwise.
The GFA also says Northern Ireland should be governed by a power-sharing executive, which the DUP is refusing to enter over in protest over the protocol.
There were also concerns that any checks on goods between NI and ROI could cause instability and threaten peace.
So a solution was needed which protected the EU's single market and the Good Friday Agreement: and so the Northern Ireland Protocol was born.
How does the Northern Ireland Protocol work?
Instead of a customs infrastructure being erected between NI and ROI - the UK's only land border with the EU - it was agreed there would be some checks on goods moving from Great Britain to Northern Ireland.
Checks on goods from England, Wales, and Scotland are carried out at Northern Ireland's ports.
It was also accepted that NI would continue following EU rules on product standards.
Fans of the protocol say it gives Northern Ireland the best of both worlds, access to the EU's single market while remaining part of the UK.
What problems is it causing?
Critics say the checks on products coming from Great Britain to Northern Ireland effectively cut it off from the rest of the UK and they are seriously affecting trade.
The Democratic Unionist Party in Northern Ireland feel so strongly about problems being caused by the protocol that they are refusing to enter a power-sharing government with rivals Sinn Fein until the issues are resolved.
Northern Irish businesses which bought products from the rest of the UK are being so severely impacted by the bureaucratic checks - which the government insists are unnecessary - that many have been forced to stop trading.
The government is unhappy with the aspect of the protocol which says goods need to comply with EU rules in order to be placed on the Northern Ireland market even when they will never enter the EU single market.
This is causing issues for businesses because they are being forced to complete new paperwork and processes, or comply with specific product requirements not relevant to them.
The UK government also takes issue with the tax rules baked into the protocol which it says is preventing Northern Ireland from being able to take advantage of changes in the rest of the UK, such as VAT cuts.
And the DUP also says the protocol is risking political stability because it impacts an aspect of the Good Friday Agreement which says Northern Ireland should remain an equal part of the UK unless a majority agreed otherwise.
What changes does the UK want?
It wants changes which minimise disruption between Great Britain and Northern Ireland by reducing the number of checks carried out.
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To do this it is proposing the formation of two trading routes across the Irish Sea: a red lane and a green lane.
Business on the green lane would be check-free and carried out by trusted traders who promise to only transport goods to Northern Ireland.
Goods which could end up in the Republic of Ireland would flow on the red lane and be subject to checks.
The UK also wants tax rules changing so Northern Ireland is more in-line with the rest of the UK.
Another demand is for an independent adjudicator to rule on disputes involving the Northern Ireland Protocol, rather than the European Court of Justice which currently carries out that function.
What's the latest?
In June last year the UK announced its intention to walk away from the Northern Ireland Protocol if a resolution could not be found, and the EU initiated legal action against Britain's bid to walk away from an international agreement.
The EU called on the UK to return to negotiations to resolve the protocol, which it did in October.
Both sides have been in talks since. But with inflation rising and public sectors striking, pressure has been piled on those in power to find a solution to allow the formation of a government which could tackle these issues.