Former cabinet minister Lord Patten has warned against a return to “old feuds” in Northern Ireland post-Brexit.
The Tory peer won support to amend the European Union (Withdrawal) Bill – requiring ministers to act compatibly with the 1998 Good Friday Agreement.
He accused opponents of his amendment of blundering into Northern Ireland politics “with a can of petrol and a box of matches in the other hand”.
In a defeat for the government, his amendment passed by 309 votes to 242.
The amendment requires ministers to act in a way that is compatible with the 1998 Northern Ireland Act and the Belfast principles.
The Belfast principles include partnership, equality and mutual respect as the basis of relationships within Northern Ireland, between Northern Ireland and the Republic and between the islands of Ireland and Great Britain.
The EU Bill will repeal the European Communities Act.
The act took the UK into the EU in 1972 and meant that European law took precedence over laws passed in the UK Parliament.
Lord Patten was spearheading a cross-party move to ensure there is no hard border between Northern Ireland and the Republic of Ireland after Brexit, and to provide continuing co-operation under the Good Friday agreement.
Lord Patten, then Chris Patten, was appointed by Labour Prime Minister Tony Blair as chairman of the Commission into Policing in Northern Ireland, one of the cornerstones of the agreement, in 1998.
He was also the Chairman of the BBC Trust until 2014.
In his speech, Lord Patten said his aim was to support the prime minister by largely re-stating government policy when some Tory MPs were keen to tip the country “over the cliffs onto the rocks” and make life difficult for Mrs May.
Mocking what he described as the hunt for a Brexit “virtual border,” he said the World Trade Organisation rules were clear that the EU, as a free trade area, had to be able to demonstrate it had a border with a country which was not a member.
Lord Patten said the border issue was closely related to the survival of the Good Friday agreement and his amendment would put the Government’s commitment to the agreement on the face of the Bill, while also making clear what was meant by a “frictionless border”.
Recalling the years of violence which had left thousands of dead and many others maimed during the Troubles, he said: “We cannot possibly want to risk going back to that.”
Lord Patten turned on those who had warned the Lords was “playing with fire” by amending the Bill, saying:
“I’ll tell you what I think playing with fire is.
“It’s blundering into the politics of Northern Ireland with a policy which is sometimes clueless and sometimes delinquent – with a can of petrol and a box of matches in the other hand.
“I don’t want to go back to the old humiliations, the old animosities, the old feuds.
“It would be shameful and dishonourable if this House was to do anything which made that more likely.
“It would be a stain on our history,” he added.
However, the former Ulster Unionist Party leader, now Conservative peer, Lord Trimble said it is “a mistake to link this process with the maintenance of peace in Northern Ireland” and doing so could be seen as “scaremongering”.
Lord Trimble accused Dublin and Brussels of wanting want a special arrangement tying Northern Ireland to the EU which would see its “link to the rest of the UK weakened”.
The Liberal Democrat Lord Alderdice, former speaker of the NI Assembly, said if the government tries to fob off Northern Ireland commitments in future legislation it will, in the minds of Irish and Northern Irish people, “justify the phrase ‘perfidious Albion'”.
Lord Eames, who is the former Archbishop of Armagh and Primate of All Ireland, warned ministers that the border issue was “extremely dangerous”.
He told peers that there was a growing apprehension in Northern Ireland that “we will be left to carry the can”.
The independent cross-bench peer said:
“There’s a lot more hanging on this debate this afternoon than simply the question of what we do with security and arrangements on the border.
“What is at stake is the reversal, or the danger of the reversal, of all that has been achieved. The peace process is still an infant growing.”
“I’m looking for the assurance which says we understand that some of the institutions and some of the achievements of your peace process are worth protecting, are worth supporting, are worth keeping in place and being allowed to develop, I want to hear that from the minister,” Lord Eames concluded addressing the Government bench directly.