Labour former Northern Ireland secretary Lord Hain pressed for legal guarantees to be built into the Bill to safeguard the 1998 Good Friday peace agreement and prevent the return of a hard border with the Republic post-Brexit.
He argued that Brexit “threatens to destabilise the fragile equilibrium in Northern Ireland”.
He added: “There are those in the Cabinet and in the ranks of the ideological hard-right who see the Good Friday agreement as a tedious encumbrance to their form of Brexit rather than the cornerstone of a hard-won peace process that is not yet complete.
“They cannot be allowed to put that at risk.”
Tory former minister Lord Patten warned there was a “real danger” that the peace process in Northern Ireland would be “blown apart” if the border issue was not settled.
The former BBC chairman said: “I think there’s a real danger here of us behaving in a way which is reckless and shameful.”
He added: “I do think in this House we should actually think about our responsibility for trying to ensure that this extraordinarily rickety construction which we’ve put together, which has kept the peace in Northern Ireland for some time, isn’t blown apart.
“There’s a real danger of that happening unless we show statesmanship and unless we have the courage to stand up for things that should really matter to us.”
Northern Ireland Minister Lord Duncan told peers in relation to the Irish border issue that there are “negotiations yet to come”.
He went on to quote country singer Kenny Rogers, telling peers: “In negotiations you must know when to hold ‘em, know when to fold ‘em, know when to walk away and know when to run.”
After a short adjournment in the proceedings for a statement on the nerve agent attack in Salisbury, Lord Adonis moved to oppose the House returning to consider the Bill in committee, complaining about the lack of breaks during the marathon debate.
Despite the Labour peer forcing a vote, on what would effectively have been the first division in the Lords on the Bill, it was dramatically halted amid confusion and committee stage proceedings resumed.
It is understood both Lord Adonis and fellow Labour peer Lord Liddle had left the chamber to be tellers and so there was no one in the chamber to object when the question to continue proceedings was put a second time and so the vote was abandoned.
A short time before Lord Adonis complained there had been no break in proceedings and argued no peers “have been guilty in any way of prolonging the debate unnecessarily”.
“I think to expect us to carry on with no break whatsoever is frankly treating the House with contempt,” he added.
Lords chief whip Lord Taylor of Holbeach pointed there had been a dinner break during the statement on the UK’s response to the nerve agent attack in Salisbury.
Later, campaigning Labour peer Lord Dubs argued for the continuation post-Brexit of a mechanism that enabled lone child refugees to join a family member living in the UK.
Lord Dubs, who came to the UK as a refugee from the Nazis, said: “It has been a positive right and a positive way to safety for some of these young people.”
He was supported by former High Court judge and independent crossbencher Baroness Butler-Sloss who said: “It would in my view be shocking if those rights were got rid of because we leave the EU.”