At least 20 members of the hardline European Research Group are expected to vote down a Brexit deal when it comes to the House of Commons next vote.
Allies of Boris Johnson have calculated that a significant proportion of the backbenchers would vote against any deal, regardless of the content in the agreement.
Among the ERG ‘Spartans’ that Number 10 fears will vote against will include Mark Francois, former party leader Iain Duncan Smith and outspoken Tory MPs Andrew Bridgen and Peter Bone.
But the Daily Mail reports approximately 100 members of the group are likely to back the prime minister.
“They know the stakes are very high for Boris as well as the country,” said an MP ally of Johnson.
“No other leader could have done more to stand up to the EU. Boris has done a brilliant job – and is still held in high esteem by party members.
“They remember what a mess we were in before he replaced Theresa (May) and don’t want to go back to that”.