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Explainer: Britain's big Brexit vote - Will parliament back PM May?

LONDON (Reuters) - If British Prime Minister Theresa May is able to strike a Brexit deal with the European Union in the coming days or weeks, she will face a crucial vote in parliament when she asks lawmakers to approve it.

Britain's Prime Minister Theresa May stands at the door of 10 Downing Street in London, Britain, October 24, 2018. REUTERS/Henry Nicholls

How will the vote in parliament work?


If a deal is agreed, May has to publish in parliament a copy of the withdrawal agreement and an outline agreement of Britain’s future relationship with the EU.

Ministers must then arrange a debate. In the directly elected lower house of parliament this will culminate in a vote to determine whether parliament has approved the deal. This is the big vote.

The government can move very quickly to organize the vote once a deal is reached, but any debate is expected to last several days.


The format of the debate and vote is yet to be decided and currently subject to fierce disagreement. This is because it could have a crucial role in determining whether the government wins the vote.

Ministers argue that any decision by parliament must be unambiguous in endorsing the deal as it is presented by the government. If not, they say the vote might not meet the legal criteria necessary for ratification of the withdrawal agreement.

But, opponents of May’s strategy instead want to use the debate to demonstrate that there is majority support for an alternative exit strategy, such as a second referendum, or remaining inside the EU’s customs union.

The way in which they are able to do this will depend on the format. There could be multiple votes which, although not legally binding, would be politically hard to ignore if they show support for an alternative exit arrangement.

A final decision on the format will be made closer to the time by parliamentary officials, based on recommendations from lawmakers. Legislation only stipulates ministers should try to hold a debate before the European Parliament has its own vote.


The unelected upper house of parliament, the House of Lords, will also debate the deal, but will only be asked to “take note” of it. The Lords will not get a straight “approve” or “reject” vote, and will not have the power to block the deal.

The legislation defining the procedure for parliamentary approval does not specify how quickly after a deal is announced the vote will happen.


Lawmakers will be voting on whether to approve a package consisting of:

1) The withdrawal agreement - a legal text setting out issues such as citizens’ rights, the financial settlement, a backstop for the Irish border, and the terms of an implementation period designed to smooth the exit process.

2) The future relationship framework - a non-legal document defining how Britain and the EU will work together in the long term on issues such as trade and security.

These two documents define the deal May and her team have been negotiating with the European Commission since June 2017.


There are 650 elected lawmakers in Britain’s House of Commons. Excluding non-voting members such as the speaker and others who never take up their seats, around 320 votes are needed to be certain of winning a vote. The actual number needed for victory depends on abstentions and absences on the day.

The vote is decided by a simple majority. Whichever side has more votes wins.


At the end of the debate, the speaker will typically ask for those in favor of the motion to shout “aye”, and then those against to say “no”. As long as some lawmakers shout “no”, the speaker will call for a formal vote, known as a division.

Votes are registered by lawmakers walking through different doorways, out of sight of television cameras and onlookers. Once the headcount is complete - which can take up to 15 minutes - lawmakers return to the debating chamber.

Four appointed tellers will assemble in front of the speaker, and one will read the result out loud.


The ruling Conservative Party has 315 lawmakers. It governs with a working majority of 13 thanks to a deal with the 10 lawmakers of the Northern Irish Democratic Unionist Party (DUP).

But May’s party is not united behind her current plan. Eurosceptics think it leaves Britain too tied to EU rules, and pro-EU lawmakers say the ties are not close enough. Both groups are potentially large enough to inflict defeat.

The support of the 10 DUP lawmakers is dependent on the solution agreed on the Irish border. They have said they will not support any deal that leaves Northern Ireland subject to different rules to the rest of the country.

The opposition Labour Party has 257 lawmakers. Led by Jeremy Corbyn, the party has pledged to vote down any deal that does not meet its criteria. The plans currently under discussion are unlikely to do this, so most Labour lawmakers can be expected to vote against May.

However, some who disagree with Corbyn’s stance could rebel and vote with the government in order to avoid the risk of leaving without a deal. Media reports have said May is courting these Labour “moderates”.

The Scottish National Party’s 35 lawmakers are expected to vote against the government deal, as are the 12 Liberal Democrats.


No. Although the vote is the focal point for resistance to the deal, the government is also required to pass separate legislation to implement the withdrawal agreement and complete the ratification process.

This legislation will be known as the EU (Withdrawal Agreement) Bill. It will be subject to full scrutiny in parliament, involving multiple rounds of possible amending and voting. It has to be passed before March 29, 2019.

This process is unlikely to be used to unpick the deal as the legislation will be implementing what has already been approved by parliament. However, if parliament feels as if May has ignored its wishes and is forcing the deal through, it could use the bill to stall the exit process.


This would be a politically explosive outcome that could topple May and her government. There are legislative guidelines on what happens next, but they could be overtaken by events.

By law, if the government motion is rejected, ministers have 21 days to set out in a statement how they intend to proceed. The government has said that if their deal is rejected, Britain will leave the EU without a deal.

It then has to call a fresh debate in parliament that could give lawmakers another chance to set out amendments - effectively giving parliament a vote on an alternative path. These amendments would not be binding, but if approved May would again find them hard to ignore.

However, it is also technically possible that the government could call a second vote in the commons and ask lawmakers for their approval again on either the same, or amended terms.

Reporting by William James; Editing by Alison Williams and Guy Faulconbridge