The Prime Minister said there was “widespread and deep” concern about the Irish border backstop as she delayed the House of Commons Brexit vote.

The Democratic Unionists are adamantly opposed to planned concessions aimed at ensuring frictionless trade across the island.

It fears the plan could create new barriers between Northern Ireland and the rest of the UK.

The unionist party’s 10 MPs are crucial to supporting the minority Conservative government, in exchange for a £1 billion dividend for Northern Ireland, but they have pledged to vote against the draft treaty with Brussels.

Here are a few questions answered.

– What was the plan for the Irish border?

A backstop solution aims to prevent the establishment of a hard border on the island after Brexit.

It would mean some regulations relating to Northern Ireland remain aligned with the rest of the EU.

It is an insurance policy if no answer can be found through a permanent trade deal after a transitional period from next March but unionists fear it could create regulatory disparity between Northern Ireland and the rest of the UK.

The backstop has been a focus of discontent with Theresa May’s draft Withdrawal Agreement with Europe.

Following the delay to the Commons vote, its future is uncertain.

– What exactly does the backstop propose?

Once the Brexit transition period ends in December 2020, the EU and the UK have agreed the backstop would apply until such a time as a subsequent agreement is in place.

This would create a single EU-UK customs territory avoiding the need for tariffs, quotas or checks on rules of origin between the EU and the UK.

Northern Irish businesses would not face restrictions when placing products on the EU’s Single Market.

– What has been the Irish Government’s reaction to the decision to defer a vote?

Irish Taoiseach Leo Varadkar has said it is not possible to renegotiate the backstop without reopening all aspects of the draft withdrawal treaty.

Dublin is keen to ensure a free-flowing border to protect the peace process and north-south trade links.

– What has been the DUP’s reaction?

Deputy leader Nigel Dodds said the vote delay was a “humiliation” Mrs May had brought on herself while Arlene Foster said the Prime Minister must get rid of the backstop.

The DUP is concerned remaining aligned to Europe would create a regulatory divergence between Northern Ireland and the rest of the UK, requiring extra checks on east-west trade and threatening the integrity of the UK as a whole.

– What have Remain voices in Northern Ireland said about the backstop?

Four pro-Remain parties in Northern Ireland including Sinn Fein and the nationalist SDLP have declared it should be “banked” rather than discarded to protect the 1998 Good Friday Agreement.

They said a no-deal Brexit would be “catastrophic”.

– What happens now?

A meeting of European leaders is planned for later this week and they will be demanding answers from Mrs May, with Europe showing no willingness to reopen months of delicate negotiations.

The Prime Minister said the risk of an accidental no agreement increased the longer it took to pass a deal.