UK ministers have been urged to end their “brinkmanship” over security in Northern Ireland after it emerged police officers from Scotland and England were to be trained for deployment there should Britain crash out of the EU without a Brexit deal.

The call from Sir Vince Cable, the leader of the Liberal Democrats, came as the issue of the Irish border and the row over the backstop – the guarantee that the border would remain open – continued to be the impasse to securing the UK-EU deal on Brexit.

Police officers, north and south of the border, are due to begin training this month after Police Service of Northern Ireland[PSNI] chiefs requested reinforcements to deal with any trouble that might arise from reviving a hard border.

But Sir Vince called on Theresa May to take a no-deal scenario off the table to avoid any return of such a hard border between Northern Ireland and the Irish Republic.

“The Brexiteers' claims that the security of Northern Ireland is not at risk as a result of Brexit have been further dismantled by these reports. In the interest of public safety, the Government must take no-deal off the table,” declared the Lib Dem leader.

"The Conservative Government's policy has been driven by the DUP who do not represent the majority in Northern Ireland who voted to remain.

"The people of Northern Ireland demand much better than this. The Prime Minister must act responsibly, end this brinkmanship, and give the people the chance to get out of this mess once and for all with a People's Vote," added Sir Vince.

The Herald asked Police Scotland for details about the special training, the number of officers involved and the costs to the taxpayer.

A force spokeswoman said she would not give answers to these questions due to “operational reasons”.

Assistant Chief Constable Mark Williams said: "All police forces in the UK are planning for the potential implications of Brexit.

"We routinely train police officers in public order to ensure we have sufficient officers ready to respond if necessary. This is part of our general commitment to supporting UK policing and is not specific to Brexit," he added.

It is thought that reinforcing the PSNI would be required in case a no-deal causes civil disorder at Britain’s own land border with the EU.

Special training will need to take place because some equipment and tactics used in Northern Ireland are different from those used on mainland Britain. The PSNI has made the request under mutual aid arrangements, which enable local forces to help each other in times of heightened demand.

Reports suggested the size of PSNI's request for reinforcements because of Brexit is around double those it has made in recent years for the marching season when additional officers are brought in to monitor and control tensions between Catholic and Protestant communities.