LONDON (Reuters) - Britain’s former Brexit minister David Davis has said up to 40 lawmakers from Prime Minister Theresa May’s party will vote against her plans to leave the European Union, meaning she may struggle to get her deal through parliament.

FILE PHOTO: Britain's Secretary of State for Exiting the European Union David Davis walks down Downing Street in London, Britain, July 4, 2018. REUTERS/Simon Dawson

The United Kingdom is due to leave the EU on March 29 but little is clear. There is so far no full exit agreement and some rebels in May’s Conservative Party have threatened to vote down a deal if she clinches one.

Davis told Huffington Post there was a “rock-solid” core of party lawmakers who belonged to the European Research Group (ERG), a grouping which wants a sharper break with the EU and were willing to vote down her plans.

The three largest opposition parties, Labour, the Scottish National Party and Liberal Democrats, have all publicly said they will oppose the prime minister’s plans.

If 40 of May’s 315 lawmakers and the opposition parties voted against a Brexit deal based on her proposals, she would fall short of the number needed to pass the legislation.

This would increase the likelihood that Britain would face leaving the EU without an agreement and of a general election or even a second referendum.

“Every group in any political party has differences, egos and so on,” Davis said.

“But with Labour voting against, the critical size of the voting bloc is quite small, it’s basically a dozen people. The rock-solid core of the ERG is a multiple of that. I’m not even an ERG member. It’s probably 30, 40.”

Under May’s proposals, Britain will seek a free trade area for goods with the EU, largely by accepting a “common rulebook” for goods and British participation in EU agencies that provide authorizations for goods.

Some Brexiteers say those proposals would ensure the EU kept control over swathes of the British economy, and thus run counter to the spirit of her manifesto pledge to leave the EU Customs Union and the Single Market.

When asked who would benefit politically if Brexit supporters felt betrayed, Davis said: “Anybody who wants to play the populist card that the elites have let you down. Populist something, whether it’s far right or far left.”