The MPs also want to force ministers to purse “transition” periods for phasing in Brexit changes that would last up to seven years – twice the length currently being sought.

The revelation is the clearest evidence yet that pro-EU Tory MPs are prepared to use their increased influence in Parliament after the election to water down Brexit.

“The numbers are there. ... There is so much legislation that will have to go through, they will have to keep everyone solid,” said a former Tory minister.

The source added that Mrs May was no longer “master to her own ship” when it comes to Brexit and will have to listen to others beyond the party’s Eurosceptic.