The Government has suffered a second blow to its Brexit bill as the Lords backed an amendment demanding Parliament has a final say on the deal.
In a vote on Tuesday evening after three hours of heated exchanges, the amendment was passed with 366 votes to 268
The bill will now go back to MPs who will decide next week whether they accept the proposed changes.
It is the second defeat the European Union (Notification of Withdrawal) Bill, has suffered in the Lords after the Government's failure last week to block an amendment that guarantees the rights of EU citizens in Britain.
Today's defeat in the Lords - which was the largest vote on record in the House - was by a slightly smaller majority than last week's vote - with a majority of 98 votes today compared to 102.
Brexit Secretary David Davis called the decision "disappointing" and said the Government intends to overturn the result.
He accused peers of trying to "frustrate" Britain's exit from the EU and said: "It is disappointing that the House of Lords has chosen to make further changes to a bill that the Commons passed without amendment.
"It has a straightforward purpose - to enact the referendum result and allow the Government to get on with negotiating a new partnership with the EU.
"It is clear that some in the Lords would seek to frustrate that process, and it is the Government's intention to ensure that does not happen. We will now aim to overturn these amendments in the House of Commons."
Prime Minister Theresa May had previously warned Britain should not commit to a Brexit that would "incentivise the EU to offer us a bad deal".
Tory former cabinet minister Lord Heseltine, a Government adviser, said the UK is facing "the most momentous peacetime decision of our time" as he backed demands for a "meaningful" vote.
Former foreign secretary Lord Hague earlier called for Theresa May to hold an early general election in the hope of securing a "decisive" majority and reduce the risk of further parliamentary stand-offs over Brexit.
But Downing Street indicated the Prime Minister would not go to the country, with a source insisting "It's not going to happen".