Britain's Northern Ireland Secretary Theresa Villiers has ruled out a referendum on Irish unity.

Sinn Féin have said that Britain voting to leave the European Union must lead to a vote on a united Ireland.

Some 56% of the electorate in Northern Ireland voted to Remain in the EU, while 44% voted to Leave.

Northern Ireland is now set to become the only part of the UK with a land border between it and an EU member.

"We have been saying all along that a Brexit would represent a hugely negative outcome for all of Ireland," Sinn Féin deputy leader Mary Lou McDonald said to Newstalk Breakfast earlier.

"The biggest issue that is now posed for Ireland is that you have 26 countries within the European Union and six counties outside. The consequences of that, I think, are self evident in terms of the border and partition. The consequences for agriculture and farmers in the north are immense, for investments in the north will be absolutely huge. I think we are now at a point where the issue of the border poll is necessary," Deputy McDonald stated.

The National Chairman of Sinn Féin in Northern Ireland Declan Kearney said: "Sinn Féin will now continue to press vigorously towards the calling for a border poll under the provisions of the Good Friday agreement."

"The landscape in the North of Ireland has been massively impacted and changed as a result of this referendum result.

"We have a situation where the north is going to be dragged out on the tails of a vote in England...The British Government have now forfeited its mandate to represent the north of Ireland in relation to the European Union," Mr Kearney concluded.

Under the Good Friday Agreement a border poll can only be called when where there is clear evidence of a public opinion swing towards Irish unity.

But Ms Villiers says that is not going to happen now.