'The British union is under challenge,' says McDonald ahead of meeting with Welsh and Scottish leaders

'We're here to create common cause with our Celtic brothers and sisters in Wales and in Scotland,' the Sinn Féin leader said

Sinn Fein leader Mary Lou McDonald: 'We live in very historic times, and for Ireland, all of this is consequential and goes to my point again, that leadership, political leadership, community leadership, business leadership in Ireland now needs to pay attention to what's actually happening, and anybody with their head buried in the sand needs to emerge from that state and look at the political horizon.'

Sinn Féin leader Mary Lou McDonald has rejected the idea that her party's collaboration with Welsh and Scottish colleagues is contrary to the running of Northern Ireland.

Ms McDonald will be in Cardiff on Monday as Sinn Féin and the lead parties in Wales and Scotland host a conference aimed at putting pressure on London to prepare for independence referendums. 

Sinn Féin's vice president Michelle O’Neill, SNP leader John Swinney and Plaid Cymru leader Rhun ap Iorwerth are expected to sign a memorandum of understanding on constitutional change that would in effect break up the United Kingdom.

However, Northern Ireland's deputy first minister Emma Little Pengelly said that Ms O'Neill had “not sought any agreement or permission from me to travel, attend or sign anything as first minister” and accused the Sinn Féin vice president of attempting to “weaponise the role of first minister”.

Speaking on RTÉ Radio this morning, Ms McDonald rejected that accusation.

"This memorandum of understanding is a high-level political accord between our respective political parties. At the heart of it is, of course, an absolute assertion of fact that it is for the people of Wales to decide the future of Wales, for the people of Scotland to decide the future of Scotland, and for the people of Ireland without interference or coercion to decide our future. That's at the core of it.

"The memorandum also recognises the many, many areas where we believe that we can collaborate and work together and share ideas in the best interest of our respective people. 

"We recognise that each of the stories — the story of Scotland, of Wales, of Ireland — have that core reality of self-determination in common, but of course each of us moves to our own pace and in our own rhythm and in accordance with, as they say, events on the ground."

Ms McDonald said the meeting is "a very significant day" and that for "anybody who hasn't noticed or hasn't taken notice, the British union is under challenge like never ever before".

"We live in very historic times, and for Ireland, all of this is consequential and goes to my point again, that leadership, political leadership, community leadership, business leadership in Ireland now needs to pay attention to what's actually happening, and anybody with their head buried in the sand needs to emerge from that state and look at the political horizon."

Ms McDonald said she wants UK prime minister Andy Burnham to see the meeting as evidence that a referendum on Irish unity is inevitable. Mr Burnham last month said a border poll was "off the table".

"This is an MOU between Sinn Féin, the SNP, and Plaid Cymru. It's between three political parties that have produced and provided the first ministers in Wales, in Scotland, and in the north, and of course that's a very historic moment.

"We're here to create common cause with our Celtic brothers and sisters in Wales and in Scotland, and we're here as Sinn Féin.

"We're here to talk about Ireland, to talk about the question of our referendums, Irish unity, and our right to self-determination. 

"And I hope that the prime minister Andy Burnham will hear that message loud and clear, and understand that far from referendums being off the table, there is now a need for Dublin and London to engage actively, and for that preparatory work to commence."

Ms McDonald said she hopes that comments from US president Donald Trump over the weekend in which he said that he would "love" to see a United Ireland, would prompt the beginning of a conversation from the Government.