A hard border in Northern Ireland would increase the terror threat and become a target for attacks, the government has been warned.
After taking evidence from MI5 behind closed doors, parliament’s Intelligence and Security Committee (ISC) said it would “not support the use of any hard border infrastructure” and called for ministers to take the risk into account.
A report published on Monday said the threat from dissident Republican groups in Northern Ireland was rated as severe, meaning further attacks are highly likely.
“The threat from Northern Ireland-related terrorism requires sustained pressure and resources must be maintained - this is more important now than ever,” it added.
“Any border infrastructure resulting from Brexit will be both a target and a recruiting badge for dissident Republican groups, who have until now used the impasse in Stormont to justify their cause and bolster their numbers.”
The ISC said security infrastructure or customs checkpoints erected at the Irish border would immediately become attack targets and increase the risk of political violence or unrest in border areas.
It said a hard border would also be “symbolic” for dissident Republican groups and become a recruiting tool to draw in young recruits.
“Brexit could also reignite the threat from Loyalist groups that have previously held a ceasefire,” the report said.
The committee referenced evidence taken from MI5 during its enquiry, but the text was redacted in the public version of the report.
Brexit makes the 300 mile border between Northern Ireland and the Republic the only point where the UK and EU will meet on land.
Under the Northern Ireland protocol negotiated last year, goods will not need to be checked when crossing the border because the country will continue to enforce the EU’s customs rules.
The protocol is due to come into force on 1 January, but there has been no agreement on how it will be implemented.
If a plan is not jointly approved by the UK and EU by the end of the transition period, parts of the controversial Internal Market Bill will come into play.
The proposed law, which breaks international obligations because parts of it violate the withdrawal agreement, gives ministers the right to overrule or ignore requirements for goods moving into Britain from Northern Ireland.
Boris Johnson did not refer to border-related issues in a statement to parliament on the ISC’s report, but he said the government would consider its findings in full and respond formally.
“Despite significant pressure from the police and security forces, demonstrated by the recent arrests targeting the New IRA, the terrorist threat they pose is enduring,” the prime minister added.
“The lines are often blurred between those involved in terrorist activity, paramilitary activity, and organised crime. In one way or another, these groups exert control over and exploit those communities for their own criminal ends.”
The ISC’s report named the New IRA as the “most widespread and capable” current dissident Republican group, and the most significant terror threat in Northern Ireland.
Since its formation in 2012, it has been responsible for a number of high-profile murders and attacks, including the shooting of journalist Lyra McKee, Derry bombing and letter bomb campaign last year.
The ISC said such groups were recruiting young people in traditionally Republican areas that had suffered from widespread poverty and unemployment.
“In these circumstances, dissident Republican groups may be able to offer young people a degree of status and purpose they feel they are lacking,” the report added.
“It is clear that the threat from dissident Republican groups will continue to endure as long as they offer an appealing, or alternative, ‘brand’ for new generations.”
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