THE Sinn Féin leader says that looking at how Scotland's MPs are treated in Westminster affirms her belief in abstentionism.

Sinn Féin's seven elected MPs do not take their seats in the House of Commons, despite repeated calls to do so during key Brexit votes.

On whether Sinn Féin would ever take their seats, Mary Lou McDonald told Andrew Marr on Sunday that the seven votes would be ineffectual and her party are resolute in their stance.

"I have no business in Westminster, we have no business in your parliament," she said.

"Westminster, correctly, advances and protects what it regards to be British interests.

"We have no business interfering in that, I am Irish, we have two parliaments and we advance Irish interests.

"I look at the experience of our Scottish colleagues and I see them at Westminster, I think there's 30-odd, and I think they would readily attest that Westminster has no interest in Scotland either, Westminster has never served Irish interests, it's not constituted to do that, Irish interests are defended in Dublin and Belfast."

McDonald added that the Good Friday Agreement would have to be revisited in the event of a hard Brexit on March 29, and an Irish unity referendum should be held.

"Put simply, if the border in Ireland cannot be mitigated, cannot be managed in the short term, well then you put the question democratically in the hands of the people and allow them to remove the border," she said.

"Bear in mind the people of the north of Ireland did not consent to Brexit."

"The backstop is the bottom line.

"On the issue of the border poll, there's no point us burying our heads in the sand and wish away a hard Brexit.

"We prepare for the worst scenario and protect our national interest."

McDonald told Marr that anyone gambling with peace on the island of Ireland is acting recklessly.

"One of the biggest symbols of success of the peace process is that people can travel unimpeded over the border.

"Any controls or checks or security checks, any question of British soldiers at the border - the taoiseach has been clear there will be no Irish soldiers on the border- no one will accept the hardening of the border on our island.

"The peace process is very solid, very robust, we are only going forward and we are not going back, it would be grossly reckless and irresponsible of the Tories to play a game of chicken with that progress.

"Peace on this island is a precious thing, shame on anybody who would play games with that."