A new Brexit deal for Northern Ireland, known as the Windsor Framework, has been adopted by the UK and the EU.

It builds on the Northern Ireland Protocol, which led to significant disagreements between the UK and European Union (EU).

Trade between Northern Ireland and the Republic of Ireland was straightforward before Brexit - both were in the EU and shared the same trade rules.

However, when Northern Ireland left the EU, a deal was required to allow trade to continue across the border.

The EU has strict food rules, and requires border checks when certain goods - such as milk and eggs - arrive from non-EU countries like the UK. Paperwork is also required for other goods.

But idea of checks at the border with Ireland is a sensitive issue because of Northern Ireland's troubled political history.

It was feared that introducing cameras or border posts as part of checks on incoming and outgoing goods could lead to instability.

Former Prime Minister Boris Johnson agreed the Northern Ireland Protocol with the EU. It became part of international law and came into force on 1 January 2021.

Under the Northern Ireland Protocol, new checks were introduced.

But rather than taking place at the Irish border, inspection and document checks are carried out at Northern Ireland's ports. This applies to goods travelling from Great Britain (England, Scotland and Wales) to Northern Ireland.

The checks apply even if the goods are due to remain in Northern Ireland.

Unionist parties - which support Northern Ireland being part of the UK - argued these checks create an effective border between Northern Ireland and the rest of the UK.

Businesses have also complained the checks mean extra costs and delays.

The new deal is aimed at significantly reducing the number of checks required.

It envisages two "lanes" for goods arriving in Northern Ireland from Great Britain:

items going through the green lane not need checks or additional paperwork.

Red lane goods would still be subject to checks.

The current bans on certain products - like chilled sausages - entering Northern Ireland from Great Britain would be removed.

Northern Ireland would also no longer have to follow certain EU rules, for example on VAT and alcohol duties.

Under the previous deal, some EU laws still applied in Northern Ireland. However, politicians at Stormont - home to the Northern Ireland Assembly - had no way of influencing them.

The new agreement introduces a so-called "Stormont brake". This would let the Northern Ireland Assembly - which creates laws in Northern Ireland - to object to new EU rules.

The process would be triggered if 30 Northern Ireland politicians from two or more parties sign a petition.

The brake could not be used for "trivial reasons" and would be reserved for "significantly different" rules.

The threshold would be "really high" according to EU law professor Catherine Barnard. "It's a security measure, but one that's not meant to be used very often," she says.

Once the UK tells the EU the brake has been triggered, the rule cannot be implemented.

The process would not be overseen by the European Court of Justice (ECJ), but it would still have a final say on whether Northern Ireland is following certain EU rules (known as single market rules).

The deal was approved by the UK Parliament, and formally adopted by the UK and the EU.

However, Northern Ireland's largest unionist party, the Democratic Unionist Party (DUP), voted against it.

DUP leader Sir Jeffrey Donaldson said the party has concerns about the Windsor Framework, but it would "continue to work with the government on all the outstanding issues".

The party also rejected the original protocol, and is still refusing to take part in Northern Ireland's power-sharing government until its concerns are addressed.