Labour has indicated it could join more than 40 Tory MPs to support a rebel plan to force a vote on new coronavirus powers.
Labour sources said it was likely the party will back a proposed amendment to the Coronavirus Act tabled by influential Tory Sir Graham Brady who is trying to force greater parliamentary scrutiny for the restrictions.
The backing increases the chances the prime minister could be defeated in a Commons vote during the six-month review of the powers scheduled for Wednesday.
Senior Conservatives and Labour MPs are among those to have added their names to the amendment from Sir Graham, the chairman of the 1922 committee of backbenchers.
If Speaker Sir Lindsay Hoyle selects the amendment that would ensure the Commons gets to debate and vote on new measures and the 40 MPs rebel, the prime minister’s near 80-strong majority would be put in jeopardy.
Conservative former party leader Sir Iain Duncan Smith, Damian Green, who was effectively deputy PM under Theresa May, liaison committee chairman Sir Bernard Jenkin, Sir Bob Neill and former Brexit secretary David Davis are among those to back Sir Graham’s amendment.
DUP MPs and the chairman of the Labour parliamentary party John Cryer are also supporting the move.
But No 10 has not signalled it was willing to make a compromise on the legislation.
“We’ve been clear throughout that it’s rightful we can take action to stop the transmission of the virus and protect the NHS.
“Both houses have the opportunity to debate and scrutinise all lockdown regulations,” a Downing Street spokesman said.