BREXIT and a hard Irish border could be the spark to light the "powder keg" of violence in Northern Ireland, UK ministers have been warned.

Northern Ireland Green leader Steven Agnew said that leaving the EU increased the "potential for violence and conflict".

Agnew issued the grave warning at the Scottish Greens spring conference in Greenock yesterday.

He said that remaining in the single market and customs union was the only solution to the Irish border issue.

Agnew claimed the UK Government had backtracked on a deal with the EU and the Irish government to maintain the free flow of goods, without border checks.

However, he said, a hard border, with checkpoints, could threaten a return to the Troubles,

He said: "In fact what looked like an agreement around regulatory alignment has now been reneged upon by the UK Government.

"It would appear the only thing that we can be certain of is uncertainty."

Agnew maintained the UK Government's insistence on leaving the customs union and single market would inevitably lead to a hard border.

He said: "What to me is clear are the options. We leave the customs union and have a hard border on the island of Ireland. We leave the customs union and have a hard border between the two islands. Or we remain in a customs union and make 'no hard border' a meaningful statement.

"It is utterly irresponsible of the UK Government to insist on leaving the customs union in the full knowledge that a hard border will be a necessary consequence.

"The progress of the last 20 years will be put at risk."

Agnew said a physical Irish border would encourage dormant terror gangs to engage in violence.

He said: "We have a relative peace it is true. But we still have violent dissident republicans. They may be small in numbers and limited in capabilities but as the IRA warned after the Brighton bomb, the terrorist only has to be lucky once.

"Loyalist gangs continue to terrorise their own communities. While they may have switched to more conventional criminality, the networks remain as does the capacity for violence.

"I have no doubt that any physical border infrastructure increases the potential for violence and conflict. Northern Ireland is a powder keg and it is a genuine fear that Brexit could be the spark that lights it."

Agnew, a member of the Northern Ireland legislative assembly, was a guest speaker at the Scottish Greens conference.

Eamon Ryan, the leader of the Irish Greens, echoed Agnew's claims in a video message to the event.

He said: "After 20 years of living without a border on the island of Ireland, we're not going to return to the old ways.

"The people of Ireland don't want Brexit – it's the last thing our island needs and we will work with those in Britain who understand the gravity of the situation to avoid this potential catastrophe."

In response, a UK Government spokeswoman said: "We remain absolutely steadfast in our commitment to upholding the Belfast Agreement in all its parts and to avoiding a hard border between Northern Ireland and Ireland."