Vital cross-Border sharing of policing expertise is going to become extremely difficult post-Brexit, former police chief Judith Gillespie has warned.

The former PSNI deputy chief constable, and member of Ireland’s Policing Authority, said Brexit would pose huge challenges.

“I think Brexit is going to pose so many challenges for law enforcement – European Arrest Warrants, exchange of information, intelligence, fingerprints, DNA, all those things,” she said.

“Any type of hard Border will have very significant costs both in the North and south.

“In the context of shrinking public-sector costs, that is going to be a real challenge – to continue to deliver policing, in the context of additional costs to policing a hard Border. It is a big concern.”

Ms Gillespie said one of the main threats to policing post-Brexit would be the sharing of important experience between the Garda and the PSNI.

Recent superintendent and chief superintendent promotion competitions have recruited a number of PSNI officers from the ranks of the Garda.

“But post-Brexit this movement of staff will become even more difficult than it is now,” she warned.

Ms Gillespie, who retired from the PSNI in 2014 after 32 years, joined Ireland’s Policing Authority in January 2016.

She said the Garda oversight body had a really important part to play “as a critical friend and in ensuring pace in delivery of change”.

“That’s important not just for the public but also for the very many good people within the organisation,” she added.

An Garda Síochána has recently been hit by a number of controversies and Commissioner Nóirín O’Sullivan has faced calls to resign.

Ms Gillespie believes the Commissioner should be given a “fair chance” to transform the force – but warned the Policing Authority will be watching her performance “very closely”.

“Nóirín is an incredibly resilient person … she has had a very difficult job to take over with the history of the organisation,” she said. “I think she has to be given time to turn the organisation around.”