Brussels/London - All eyes will be on the British parliament during the crucial votes on Prime Minister Theresa May's plans for Brexit, after a crushing defeat of the deal she reached with Brussels.

The votes will pave the way for a second vote on the withdrawal agreement and an accompanying political declaration after parliament's main elected house, the Commons, voted against the deal by 432 to 202 on January 15, delivering the biggest-ever defeat to a British government.

EU officials say the Brexit deal is not up for renegotiation, but few doubt that they will do everything they can to prevent Britain from crashing out of the European Union without measures in place for an orderly departure.

Here are some of the possible scenarios:

A) PLAIN SAILING

Parliament approves the withdrawal agreement and the political declaration on future negotiations, which have been endorsed by EU member states. The European Parliament also ratifies the texts and they are in place to ensure a smooth transition when Britain leaves the EU on March 29.

From the outset, this outcome looked unlikely. Since parliament began debating the Brexit package, the odds have fallen further.

B) ROUGH WATERS

Parliament narrowly rejects the deal. May returns to Brussels to seek the "clarifications" she has said she needs in order to put the agreement to a third vote.

The EU has made clear that the fundamentals of the withdrawal deal are not up for renegotiation, so any changes would likely be cosmetic.

If May gives up trying to rally pro-Brexit rebels behind her deal, she could opt for a softer Brexit - for example by keeping Britain in the EU's customs union - in the hope of winning the votes of Labour lawmakers who want Britain to stay more closely aligned with the bloc. This would likely be an easier sell in Brussels but would enrage the Brexiteers in her party.

C) MUTINY

If parliament overwhelmingly rejects the deal for a second time, May's leadership could come into question again, potentially bringing Britain closer to a general election. It would also strengthen the hand of those campaigning for a second referendum on Brexit.

To avoid an unregulated Brexit in March, Britain may seek an extension of the two-year Brexit negotiating process. Many Labour and pro-EU Conservative lawmakers are expected to back an amendment that seeks to steer the government in this direction.

Some opponents of the Brexit deal argue that other options are available. These range from a "managed no-deal" scenario with a series of mini-deals to regulate key areas such as medical supplies and aviation, to temporary membership of the European Economic Area (EEA) alongside other non-EU members such as Norway.

D) THE WORST-CASE SCENARIO

If the British parliament does not accept the withdrawal deal and it cannot be ratified before March 29, this would put Britain on track for an unregulated Brexit.

EU rules would cease to apply in Britain as of March 30 and the country would drop out of shared arrangements, such as common air traffic rules or trade deals with third countries.

Businesses and people would likely suffer from administrative chaos and backlogs at Britain's borders.

British eurosceptics say such predictions are part of a "project fear" to persuade people to accept the deal.

E) NO BREXIT

The European Union's top court ruled in December that Britain has the right to change its mind about Brexit. This has emboldened those calling for a second referendum.

May has already warned parliament that the choices it faces are "this deal, no deal, or no Brexit."

However, remaining in the EU would also be a tricky endeavour at this stage and would likely leave Britain even more divided.