How far did parliament influence Brexit legislation?

Parliament’s role in the Brexit process has been the subject of widespread controversy among politicians, commentators, and experts. This makes it important to understand exactly what kind of influence parliament wielded in that period. Tom Fleming and Lisa James shed new light on this question by summarising their recent article, Parliamentary Influence on Brexit Legislation, 2017-2019, as published in ‘Parliamentary Affairs’.

Parliament’s role in the Brexit process was – and remains – highly controversial. But despite this controversy, there is widespread agreement that parliament was unusually influential during this period, and particularly during the hung parliament that lasted from 2017 to 2019.

This verdict is largely based on parliament’s high-profile impact on the Brexit negotiations, where MPs famously torpedoed Theresa May’s exit deal, and delayed the UK’s eventual departure from the EU on multiple occasions. But parliament also considered a raft of important Brexit-related legislation, which aimed to unravel the UK’s membership of the EU and create new domestic regulatory frameworks. This legislation has been less studied, but is crucial to our understanding of the relationship between parliament and government in this period.

Our recent article therefore explored the extent and nature of parliament’s influence on this Brexit-related legislation. We did so by analysing the parliamentary passage of the 13 Brexit-related bills introduced in the 2017-19 parliament, including the fate of over 3000 proposed amendments.

More specifically, we explored three different mechanisms by which parliament can influence government legislation: passing non-government amendments; forcing government concessions; and influencing the government’s approach through ‘anticipated reactions’. For each mechanism, we investigated its prominence between 2017 and 2019, and compared this to evidence from earlier periods.

Non-government amendments

Maybe the most obvious way for parliament to influence legislation is by passing non-government amendments. Opposition parties and government backbenchers can propose changes to government bills at multiple stages of the legislative process. However, such amendments are almost always defeated, so are rarely an effective vehicle for parliamentary influence.

We might reasonably expect non-government amendments to have been more successful than usual during the Brexit period, given the government’s lack of a Commons majority, deep divisions in the Conservative Party, and a greater openness to cross-party cooperation among the government’s opponents. Indeed, some high-profile government defeats did take place, particularly as MPs sought a statutory ‘meaningful vote’ on the final Brexit deal.

Yet despite this, non-government amendments were not notably more successful than normal. Such amendments had a success rate of just 1.4% in the Commons, and 4.2% in the Lords: figures which don’t differ dramatically from findings in previous work. Some non-government amendments made important changes to Brexit legislation, but the overwhelming majority – as usual – had no direct impact at all.

Government concessions

Parliament can also affect government legislation in a second, subtler way: by forcing government concessions. In particular, parliamentary pressure – expressed through tabling of non-government amendments, select committee recommendations, speeches in the chamber, or behind-the-scenes lobbying – can force ministers to propose amendments to their own legislation. Such concessions allow the government to respond to parliamentary concerns without the political embarrassment (and, occasionally, the imperfect drafting) that might come from simply accepting non-government amendments.

The difficult parliamentary context after the 2017 general election, with the government often at risk of losing Commons votes, should in theory have heightened pressure for concessions of this kind. But both Theresa May and Boris Johnson have been accused of taking an inflexible and confrontational approach to parliament, and resisting MPs’ attempts to influence the Brexit process. This could suggest that, contrary to the parliamentary logic, the government might have been less willing than usual to make concessions.

Our evidence suggests that parliamentary pressure did lie behind many of the changes made to Brexit legislation in this period. Across the 13 Brexit bills, we identified 190 successful amendments which were formally proposed by the government and made meaningful changes to the relevant bill’s substance, on topics ranging from sanctions to scrutiny of delegated legislation. A clear majority of these amendments (65% in the Commons, and 92% in the Lords) could be traced to earlier parliamentary pressure.

This is again consistent with earlier work that found a majority of substantive changes proposed by ministers had their origins in pressure from non-government parliamentary actors. Though – for reasons the paper explains – comparing different time periods is not totally straightforward, our analysis suggests that there may even have been more government concessions in the 2017-19 parliament than in earlier periods.

Anticipated reactions

Rather than responding to parliamentary opposition by accepting non-government amendments or bringing forward concessions, ministers may wish to avoid that opposition in the first place. They often aim to achieve this by considering parliament’s likely reaction to a bill in advance, and shaping their proposals accordingly.

This form of parliamentary influence can be tricky to detect, so is often underestimated. However, one visible form of ‘anticipated reactions’ comes when the government ‘pauses’ or entirely withdraws legislation that has already been introduced to parliament. This is typically a rare occurrence, but usually reflects ministers looking ahead and reacting to anticipated defeat or amendment.

The same factors that conditioned our expectations about government concessions also apply here – the realities of a hung parliament, versus the inflexible approach of May and Johnson. But it is also relevant that the typical strategy of prime ministers with only a slim working majority – simply avoiding controversial legislation in the first place – was not available in the 2017-19 parliament, given Brexit’s status as the central plank of government policy. This might suggest that controversial legislation was likely to be introduced, but risked being abandoned when it ran into parliamentary difficulties.

Delays of this kind were strikingly frequent during the Brexit process. Of the 13 bills we studied, seven failed to become law before the 2019 general election. Five bills introduced by Theresa May’s government had entirely stalled by winter 2018 or spring 2019 – the span of time when May’s Brexit deal suffered multiple defeats and the extent of the deadlock in the Commons became evident. These bills were not voted down by MPs or peers – the delay resulted from the government refusing to bring them forward for further consideration. In September 2019, when questioned on the whereabouts of paused bills, then Leader of the House of Commons Jacob Rees-Mogg explained that ‘there is no certainty that these Bills will get through without doing things that are contrary to Government policy, and therefore it is unlikely that they will make progress’. This suggests that this strategy was motivated, at least in part, by a fear of possible future amendments.


Our article systematically identified the extent of three different mechanisms of parliamentary influence over Brexit-related legislation. The resulting analysis uncovered two main patterns.

First, we found a large degree of continuity with earlier periods. Parliament had sizeable influence on this legislation, but it came predominantly through triggering government concessions. Non-government amendments remained largely unsuccessful.

Second, however, our analysis of parliamentary influence through ‘anticipated reactions’ revealed a major change from earlier periods. This was the amount of legislation that the government simply paused in the face of anticipated parliamentary opposition. Here, parliamentary influence was in tension with executive control of the legislative timetable. MPs and peers may have been keen to amend the legislation – but the executive could abandon bills rather than giving parliament an opportunity to do so. As a result, any additional parliamentary influence on legislation in this period was more preventative (deterring legislation) than constructive (rewriting it).

This post is a summary of a much more detailed article, which is available to download.

About the authors

Tom Fleming is a Lecturer in British and Comparative Politics at UCL.

Lisa James is a Research Fellow in the Constitution Unit. Her book with Meg Russell, The Parliamentary Battle over Brexit, will be published by Oxford University Press in March.

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