The leader of Northern Ireland’s Ulster Unionist Party has urged members of the Republic of Ireland’s leading political party to be cautious of their words when it comes to Brexit.

Robin Swann sounded the warning as he addressed a side event at the Fine Gael annual conference, Ard Fheis, in Dublin.

He said while relations between the two parts of the island have improved in the last two decades, Brexit has caused a strain, adding that some comments made by Fine Gael members recently have been received like a “poke in the eye” by unionists in Northern Ireland.

Mr Swann said he wants to see relations improve – but that means being honest with each other.

Fine Gael conference
UUP leader Robin Swann, left, with Irish Justice Minister Charlie Flanagan during the event (Tom Honan/PA)

“Good neighbours must be honest with each other, and that means speaking up when you think the other has overstepped the mark,” he said.

Irish Justice Minister Charlie Flanagan and Business Minister Heather Humphreys were in the audience for his address.

Former SDLP leader Alasdair McDonnell, ex-Alliance Party leader John Cushnahan, Ulster Unionist MLA Steve Aiken and former Ulster Unionist MP Danny Kinahan were also present.

Mr Flanagan extended a warm welcome to Mr Swann and the other visitors from Northern Ireland.

He said they should feel able to speak freely and emphasised that both he and his party “care very deeply about Northern Ireland”.

The former Irish foreign affairs minister said at one stage he was spending more time in Belfast than in his own constituency.

He said as Justice Minister he is now focused on security, and welcomed what he termed the “historic high” in co-operation between the Police Service of Northern Ireland and An Garda Siochana, at which point he paid tribute to Garda Commissioner Drew Harris, a former PSNI officer.

On Brexit, Mr Swann said his party wants to see the “best deal possible for the UK, and with that Northern Ireland”.

He added that while the Irish Government said they want to see a deal that protects Northern Ireland too, it has “not felt like we were working to achieve the same objective”.

He said: “To be honest, comments from members of this party sometimes were delivered like a poke in the eye to unionists.

“Our party has been clear that we do not want to see the reintroduction of physical structures at the border on the island of Ireland.

“But we did not see the same understanding from your government for our concerns about a hard border in the Irish Sea and problems that created for us both as unionists and as an economy which relies heavily on our place in the United Kingdom’s single market.

Fine Gael conference
Mr Swann urged better co-operation with Ireland on Brexit (Tom Honan/PA)

“A sea border is a direct challenge to the Belfast Agreement and the principle of consent and is not a concern that should just be waved away.

“Given that, at this time, it seems very unlikely that the current withdrawal agreement will progress, there must be a change in tact from your Government and other parties in the south.

“Selective reading of the Belfast Agreement and ‘Ireland first’ rhetoric will only serve to stretch relationships.

“The reality is that the geography of these islands means we rely heavily on each other.

“An aggressive negotiating stance now may lead to adverse consequences in the future.

“A bad deal, or no deal, with be catastrophic for us all.

“It is in all our best interests that a withdrawal agreement and future relationship is reached that works.

“In the weeks ahead I would urge caution over language, and to have thought for how statements and soundbites will be heard in Northern Ireland – as Terence O’Neill once put it, ‘sensible restraint and common prudence’.

“I spoke recently at Queen’s University and I delivered the same message to unionism – that we must be careful with our words.”