LONDON (Reuters) - British Prime Minister Theresa May needs to win approval for her Brexit deal in parliament on Dec. 11. But critics are lining up on all sides to say they will oppose it and the chances of the government winning a vote currently look slim.

FILE PHOTO: Demonstrators protest against Brexit outside the Houses of Parliament in London, Britain, November 28, 2018. REUTERS/Henry Nicholls/File Photo

So what happens if she loses the vote?

By law, if the deal is rejected, ministers have 21 days to state how they intend to proceed. The government has previously said that if the agreement is rejected, Britain will leave the EU without a deal.

In reality, the huge uncertainty in the world’s fifth largest economy and a likely adverse reaction from financial markets would necessitate a much quicker political reaction.

Below are some possible next steps:

RESIGN

May could resign as leader of the Conservative Party, triggering an internal contest to replace her without a general election. She has said she still expects to be prime minister in two weeks.

OUSTED

A long-running effort by some members of May’s own party to get rid of her could gain renewed impetus. If 48 out of 315 Conservative lawmakers want her to go, the party holds a leadership ballot. If she loses, there is an internal contest to replace her without a general election.

RENEGOTIATE

The government could try to renegotiate the terms of the deal, seeking extra concessions from the EU, and then call a second vote asking lawmakers for their approval on amended terms. May and the EU have said the deal will not be reopened.

VOTE OF NO CONFIDENCE

The opposition Labour Party could call a vote of no confidence in the government, seeking to take control of the country without holding an election.

If a majority of lawmakers vote against May’s government, Labour would have 14 days to prove, by a vote, that it could command a majority and form its own government.

BACK TO THE BALLOT

If May’s government loses a confidence vote and Labour is unable to form a new government, an election is called. May could also call a general election herself if two-thirds of lawmakers in parliament agree to it. May has said that a general election is not in the national interest.

LONGER-TERM OPTIONS:

SECOND REFERENDUM

The route to a second referendum on Brexit is unclear, but a vocal contingent of lawmakers in parliament support such a step. May has said she will not call a second referendum.

DELAY OR CANCEL BREXIT

The government could seek to extend the negotiating period with the EU to give it time to try to reach a better deal, hold a general election, or conduct a second referendum.

The government could also try to withdraw its notice of intention to leave the EU - something that a European Court of Justice advocate general said was allowed, in a formal but non-binding advice document that the ECJ can usually be expected to follow.

May has said she does not want to delay Britain’s exit from the EU, and will not revoke the notice of intention to leave.