Shadow Chancellor John McDonnell has risked new anger from unionists by declaring that he “longs for a united Ireland”.

The Labour frontbencher’s words come at a critical moment when the Irish border and the future of Northern Ireland are at the centre of the of tension in Brexit talks.

He did also say that the Brexit process should not put the Good Friday Agreement and the Northern Ireland peace process at risk.

But Mr McDonnell has previously been forced to apologise over praise he has given to the IRA and its “bombs and bullets”.

He was speaking at a lunch event in Westminster, when he was asked about his historic and well known views on Irish Republicanism, telling journalists: “You know my background, I’m a Republican.

“I long for a united Ireland but I recognise democracy, and Ireland will not be reunited around some contortions over the relationship with the EU.

“It will only be reunited on the basis of the popular support of the Irish people and that is what I respect.”

With time running out, Brexit negotiations stand on the brink of collapsing over the inability of negotiators to find a way to prevent a hard border on the island of Ireland after the north leaves the EU.

But Mr McDonnell did stress that the protection of the peace process was paramount. He said: “One of the concerns that we’ve got is that nothing in these discussions should in any way cause any damage to the Good Friday Agreement or its implementation which was a huge achievement.”

He added that if Tony Blair had “stopped there” instead of going on to the war in Iraq, he “would have been remembered as one of the most consequential prime ministers.”

The shadow chancellor has previously caused controversy when he called for former IRA militants to be “honoured” during an event to remember the death of hunger striker Bobby Sands.

Speaking in 2003 he said: “It’s about time we started honouring those people involved in the armed struggle. It was the bombs and bullets and sacrifice made by the likes of Bobby Sands that brought Britain to the negotiating table.

“The peace we have now is due to the action of the IRA. Because of the bravery of the IRA and people like Bobby Sands, we now have a peace process.”