LONDON (Reuters) - Britain’s main opposition Labour Party are expected to back a proposal on Tuesday that could mean the government needs parliamentary approval for a no-deal Brexit, putting up a new hurdle for Prime Minister Theresa May.

Anti-Brexit protestors gather outside Downing Street, on Whitehall in central London, Britain January 2, 2019. REUTERS/Henry Nicholls

Britain is due to leave the European Union on March 29, but the deal May has negotiated with the bloc looks unlikely to be approved by lawmakers in its current form, generating huge uncertainty about the path of the world’s fifth largest economy.

Preparations for leaving without a deal - the default scenario if May’s agreement is rejected - have been ramped up, with government and businesses activating and testing contingency plans designed to limit the expected disruption.

That has prompted a group of lawmakers from across the political spectrum to come up with a plan to try to win parliament the authority to prevent a no-deal exit by amending legislation.

The plan, if successful, would mean that parliament would need to explicitly approve a no deal exit before the government could exercise certain powers it would need to implement one.

The amendment to a bill that is designed to implement the budget and gives the government authority to keep its tax raising powers intact after Brexit could be put before parliament on Tuesday if it is chosen by the speaker.

Tax is just one in a long list of areas in which the government needs to make changes to legislation to disentangle Britain from the EU after more than 40 years of membership.

A Labour source said on Monday the party was expected to vote in favour of the amendment.

Because May does not have an outright majority in parliament to rely upon, and her own Conservative Party is split over Brexit, Labour’s support would give the amendment a chance of passing if enough Conservatives also support it. Several have already signalled their backing by co-sponsoring the amendment.

It would not be an outright block on Britain leaving without a deal, but would create both a political and technical headache for the government.

“Practically, it constrains the government’s ability to do certain things if a no deal happens. What it doesn’t do is stop no deal,” said Joe Owen, associate director of the Brexit programme at think tank the Institute for Government.

“Politically, it could be quite important as a firm crystallising of a majority against no deal.”

A spokesman for May said the government would consider amendments as it usually does, but it was important that ministers were able to deliver Brexit, including in a no-deal scenario.