Plans to deploy police from other forces to Northern Ireland in the event of a no-deal Brexit have been cautiously welcomed by the body that represents rank-and-file PSNI officers.
The contingency plans by ministers are part of a policing procedure known as mutual aid, in which officers can be deployed to other parts of the UK to assist during emergency situations.
Previous examples include the 2013 G8 summit in Fermanagh and the London riots.
Mark Lindsay, chairman of the Police Federation for Northern Ireland, said any support in the event of a deteriorating security situation following Brexit would be welcomed.
However, he has warned that the policy is not "a sustainable solution to the resourcing problem", in the event of additional challenges caused by Brexit.
Reacting to the report in the Sunday Times, he said: "This procedure is nothing new, mutual aid has been on the books since the G8 summit and during annual parading issues.
"We would welcome any sort of numbers, but these don't come without a resourcing cost. We have to deploy PSNI officers along with these mutual aid officers."
It is believed up to 300 police officers from Scotland would initially be called upon to assist the PSNI if required, with further numbers from forces including London's Metropolitan police on standby. Mr Lindsay added that any such deployment would likely be sent to other parts of Northern Ireland so that more locally-trained officers can be prioritised for any border operations.
He said: "As to where they would be deployed, that would all be properly risk-assessed.
"They would potentially be deployed to other areas to allow PSNI officers to be deployed on the border.
"We would obviously like to have our own officers, but in the absence of that, mutual aid has to be one of the options.
"We have consistently said that the recommendation in the Patten Report of 7,500 officers is what we would be looking for".
Calum Steele, general secretary of the Scottish Police Federation, warned that PSNI officers were better equipped to deal with an upsurge in terrorist activity than those from outside.
He told the Sunday Times: "The risk of a no-deal Brexit to police officers working in Northern Ireland, regardless of what part of the United Kingdom they are from, is an unacceptable risk, and everything humanly possible should be done to avoid a no-deal Brexit.
"While Scottish police have been through training in Northern Ireland public order tactics, the simple reality is that our officers are not armed when they go to Northern Ireland and are not trained to the same level of terrorism awareness as officers in Northern Ireland.
"They are slightly less able to identify the threats as immediately as those officers in the theatre because they don't have the same training in counter-terrorism."
DUP MP Sir Jeffrey Donaldson described the plans as "old news" and said he did not believe there would be any installation of border infrastructure in the event of no-deal.
He said: "Both the Irish Government and British Government have made it clear there will be no infrastructure on the border. Those who use this as a scare tactic are only giving succour to dissident republicans."
At the G7 summit in Biarritz yesterday, Prime Minister Boris Johnson said the prospect of a Brexit deal is "touch and go" but failure to reach an accord would be the fault of the European Union.
The PM said he believed the chances of a deal were "improving", but warned that progress "depends on our EU friends".