Following today’s Supreme Court judgement, the focus of attention shifts back to parliament.  How long will it take for parliament to pass the necessary legislation? How likely is it that the legislation will be amended? Robert Hazell and Alan Renwick assess the implications for the Brexit timetable, and the government’s negotiating strategy.

What will happen to the government’s timetable?

The government have confirmed that they will introduce a short bill, probably just one or two clauses, which it will seek to pass as a matter of urgency. Bills have occasionally been passed through parliament in a few days, or even a few hours. But that can only happen if both chambers recognise the urgency, and support the bill. Crucially, the government would need to get majority support for a timetabling motion in the House of Commons to expedite the process. That might not be forthcoming in a House where three quarters of MPs voted for Remain. (In 2012 Nick Clegg had to abandon his Lords Reform bill after the government lost the timetabling motion following a big Conservative rebellion).

In the House of Lords, the government has no majority, and no control over time. The Lords Constitution Committee and the Lords EU Committee will both want to scrutinise the bill and its implications. The Lords will not block or wreck the bill, but they will want to give it proper scrutiny; especially if they think the scrutiny in the Commons has been inadequate.

Can the bill be amended?

In November government sources suggested the bill would be ‘bombproof’. Parliamentary officials say that is a fantasy. All sorts of ingenious amendments can be tabled, on process as well as substance: requiring a white paper to be published setting out the government’s negotiating position; seeking a second referendum on the negotiated terms; requiring the government to acknowledge that Article 50 notification is revocable, etc. Debate risks exposing continuing splits within both the Conservative and the Labour parties. Because the referendum specified nothing about what Brexit means, the battle continues between Brexiteers, who mostly support a hard Brexit, and Remainers hoping for a soft Brexit. Meanwhile Labour remains split on how to respond to the referendum outcome – to respect the will of the 52 per cent (who make up a majority in constituencies such as Stoke-on-Trent Central, where the forthcoming by-election will be hard fought), or speak up for the majority of Labour voters, who backed Remain. Speaking in parliament after the judgement, Labour’s Shadow Brexit Secretary, Keir Starmer, indicated that Labour would seek to amend the Article 50 legislation to require a white paper on the government’s plans, stipulate mechanisms for parliamentary scrutiny of the negotiations, and hold a ‘meaningful’ vote on the final deal. Legislation gives all groups in parliament multiple opportunities to table amendments or extract promises or impose conditions on the government during its passage.

What is the balance of forces in parliament, and within the main political parties?

Few doubt that the government will get an Article 50 bill through.  How easy a passage it receives will depend largely on the Labour Party: Jeremy Corbyn has indicated that Labour will support the bill, though dissent on his benches appears to be becoming more pronounced. Around 75 per cent of MPs supported Remain during the referendum; in the Lords the proportion of Remainers is even higher. The key constraint in the Commons is on the Conservative benches. The government has a working majority in the Commons of only 16. If there are amendments tabled which could unite all the other parties, it would only take a rebellion from a dozen or so Conservative MPs for the government to lose.

Following the Prime Minister’s Lancaster House speech, rebels are more likely to be Remainers than Brexiteers. They will seek to maximise access to the single market, and other benefits of EU membership.  They will seek clarification of what exactly Theresa May meant about the different options for a customs union, the feasibility of reaching agreement over the next two years about our future relationship as well as the terms of departure, the timescale for interim arrangements, and protection for vital sectors such as financial services.

The government will be reluctant to go beyond Theresa May’s 12 broad objectives for fear of compromising its negotiating strategy.  It will also be reluctant to exacerbate the continuing splits within the Conservative Party. But legislation could force the government to disclose rather more of its negotiating hand. The preponderance of Whitehall advice (especially from the Treasury) will have been to seek a soft form of Brexit, retaining access to the single market, or at least remaining within the customs union. MPs and peers might use the debates to try to force disclosure of this advice, and to require the government to make regular reports to parliament of the progress of the negotiations.

Can Brexit be delayed, or even stopped?

The strong expectation is that the government will get its bill through. Brexit will not be stopped by the Supreme Court’s ruling. The only way it might be stopped is if negative evidence emerges about the consequences of Brexit, or if the government fails to deliver what it has promised from the negotiations.  At present there is little sign of any shift in public opinion: the polls continue to suggest that if the referendum were re-run, it would come to broadly the same result. But it is impossible to predict how opinion might shift over the coming two or more years – for example if it becomes clear that more and more businesses are relocating to the continent, or if the negotiations go badly.

What about the Great Repeal Bill?

This is not the same as legislation to authorise the government to trigger Article 50. At the Conservative Party conference in early October, Theresa May announced that in the next session of parliament, in 2017–18, the government would introduce a Great Repeal Bill to repeal the European Communities Act 1972. That bill is necessary to ensure that EU law no longer has effect in the UK. It would take effect on the day that the UK leaves the EU: on the government’s proposed timetable, in 2019. Legislation to trigger Article 50 will be on a much faster timetable, in the coming weeks, and with a different purpose: it will initiate the UK’s departure from the EU, while the Great Repeal bill would conclude and give effect to it.

Will there be an early general election?

Theresa May ruled out any need for a personal mandate when she became Prime Minister in July. She might need a new mandate if her party remains divided, or if the process of getting parliamentary approval becomes rocky at a later stage. But she cannot simply call a snap election: the Fixed-term Parliaments Act 2011 abolished the prerogative power of dissolution. Under the Act, it would require two thirds of all MPs to vote for dissolution, or for the government to be defeated on a formal no confidence motion. The first of these is a very high threshold, unreachable without cross-party support. But it might be difficult for Labour to oppose, given their own calls for an early election, and the added attraction that it would avert the current boundary review in which many MPs risk losing their seats. The second route, defeat on a confidence motion, might be followed if Theresa May called a confidence motion to rally support for one of the necessary Brexit bills, and lost; or if she engineered defeat on such a motion. The only other option, if Theresa May wants to remove the obstacle to an early election, would be to introduce legislation to repeal or amend the Fixed-term Parliaments Act – but that would be more difficult, as it would need to complete its passage through both chambers.

A fresh general election would not necessarily resolve what form Brexit should take. It would require the Conservatives to present a united front; or if they are disunited, for sufficient Conservatives loyal to the government’s negotiating line to win, to make it clear which view should prevail. It would also bring the splits within Labour to the fore.

Will there be a second referendum?

The Liberal Democrat leader Tim Farron has said his party will only support legislation authorising the government to trigger Article 50 if the government promises a second referendum on the terms of Brexit once the negotiations are concluded. Although a strong democratic case can be made for a second referendum, given the momentous consequences, it currently looks unlikely to happen. The two year timetable for the Article 50 negotiations is already extremely tight. The EU27 are pressing the UK to get on with it, and may be reluctant to extend the two year deadline. A second referendum would require separate legislation, which would delay matters further. If the intention was to allow voters to reverse their previous decision on Brexit, this would be possible only if it were clear by then that Article 50 notification can be revoked – probably requiring a ruling from the European Court of Justice. Instead the government has offered a vote in both parliamentary chambers on the final deal. It appears to be proposing a take it or leave it vote: that, if parliament rejects the package, the UK would leave the EU on World Trade Organization terms. Whether that would really be the outcome is unclear: the government might well fail to survive such a defeat; in which case the final consequences would depend on who subsequently entered power.

About the authors

Robert Hazell is Professor of Government and the Constitution at the Constitution Unit.

Dr Alan Renwick is the Deputy Director of the Constitution Unit.