Brexit Secretary David Davis has reiterated his commitment to avoid a hard border on the island of Ireland after Brexit, amid an ongoing row over customs arrangements.
He told MPs at Brexit questions: "We have said categorically that there will be no physical infrastructure or related checks and controls at the border between Northern Ireland and the Republic of Ireland.
"We've set out our clear commitments on borders and put forward two potential customs models, which were just referred to earlier.
"Now, I've always said the best solution to solve the Northern Ireland, Ireland border is through the deep and special partnership between the United Kingdom and the European Union, recognising the unique circumstances of Northern Ireland.
"As the European Commission itself has acknowledged, solutions to the Northern Ireland border cannot be based on precedent."
He was speaking after peers in the House of Lords voted to give MPs the power to stop any Brexit deal that might restore a hard border.
The upper house supported an amendment to the EU Withdrawal Bill that would bar the introduction of border checks and any form of physical infrastructure without the prior agreement of the Irish Government.
It is the tenth occasion in recent weeks that Theresa May's government has been defeated in the Lords on Brexit legislation.
Earlier, Mrs May asked officials to draw up revised proposals for the UK's customs arrangements post-Brexit, after senior ministers strongly opposed her preferred "customs partnership" option.
Mr Davis was also pressed over the delays among ministers in agreeing the UK's future customs arrangements with the EU.
The Brexit Secretary said: "The simple truth is that this is a complex and important issue.
"It will affect the future of our country generations into the future. It has direct effect on the sensitive issue of Northern Ireland and the peace process there, which we are committed to protect at all costs.
"And so there's no surprise that it takes some time to absolutely nail down this policy."
Mr Davis later told MPs that the chances of the UK leaving the customs union on exit day were "100%".
Meanwhile, voters will today pass judgement on Mrs May's Conservative party in local government elections across England.
The polls will decide more than 4,400 council seats, determining the makeup of 150 local government authorities.
Just over 40% of the seats are in London - where polls suggest a swing towards the opposition Labour Party.
A Westminster by-election is also taking place in West Tyrone to fill the seat vacated following the resignation of Sinn Féin's Barry McElduff.
The elections will be viewed as a gauge of support for Mrs May at a time when she is facing a possible revolt over her Brexit strategy and a scandal over immigration policies that has already forced the resignation of one of her closest allies.