One of British Prime Minister Theresa May's predecessors attacked her Brexit strategy on Monday as a bill to start the EU divorce also hit opposition in the House of Lords.
Former Conservative prime minister John Major said May's government was peddling an "over-optimistic" view of Brexit and said it was "time to stop" the criticism of those who disagreed with her plans.
The outspoken attack came as May prepares to start negotiations on leaving the European Union by the end of March, following the June referendum vote last year to quit the bloc.
Major warned that those who could least afford it would suffer from May's plan to take Britain out of Europe's single market, and said her government was not being honest.
"I have watched with growing concern as the British people have been led to expect a future that seems to be unreal and over-optimistic," Major told the Chatham House think tank.
He also chastised her approach to negotiations with other EU leaders, warning: "A little more charm, and a lot less cheap rhetoric, would do much to protect the UK's interests."
May cannot trigger Article 50 of the EU's Lisbon Treaty, starting a two-year countdown to the divorce, without parliamentary approval.
A short bill empowering her to start the negotiations cleared the House of Commons last month, but on Monday members of the unelected upper House of Lords began debating changes that could cause a delay.
The first crunch vote could come on Wednesday on an amendment to guarantee the rights of more than three million Europeans currently living in Britain.
Another is expected next week on enshrining into law the government's promise to give parliament a vote on the final Brexit deal.
Government supporters have warned the chamber risks abolition if it is obstructive, but a Lords source in the opposition Labour party told AFP that May was on course to "lose handsomely".
If peers succeed in amending the legislation, it will have to go back to the Commons for approval, making May's end-of-March deadline very tight.
May's Conservatives have a majority in the House of Commons, but the party has just 252 peers out of around 800 in the House of Lords.
Former minister Michael Heseltine is among the Tory rebels who could join Labour and the pro-European Liberal Democrat party in backing moves to give parliament a final vote.