The Government's highly anticipated, formerly 'Great', Repeal Bill – to be published this Thursday,13 July 2017 – is likely to be the most constitutionally significant legislation enacted by the UK Parliament since the European Communities Act 1972, which took the UK into the European Economic Community and which the Repeal Bill is set to repeal and replace.

In this blog, we look ahead to what the Bill is expected to do, what happens next and the consequences of Parliament failing to pass the Repeal Bill into legislation before the UK leaves the EU.

Why is the Repeal Bill so important?

Leaving the EU will require the most comprehensive re-writing of the UK's statute book ever undertaken. Parliament must unpick over 40 years of integration between the UK and the EU legal systems and ensure no gaps are left in the process.

Currently, some key elements of the law applying in the UK (particularly business regulation) are actually EU laws that apply directly to UK businesses. Other elements are UK laws that are based on EU laws. When the UK leaves, unless there are changes to UK domestic law, certain EU laws that currently apply directly in the UK will fall away, while other UK law that gives effect to EU law will continue to apply even though the UK is no longer a part of the EU system on which the UK law is based.

Unless the UK passes new laws to say what should happen in areas currently handled by the EU, there will be gaps in the rules (often in areas where everyone would agree there should be rules) and significant legal uncertainty as to how the remaining rules should apply in a post-Brexit UK.

In short, without something being done, there is a risk of legal chaos.

The Repeal Bill is the Government's plan to address this challenge by preparing UK law for the UK's withdrawal in March 2019 to ensure maximum legal certainty and stability. It will break the constitutional link between the EU and the UK, while at the same time transposing much of the detailed rules of the EU directly onto the UK's statute books.

For a visual explanation of how EU law is currently incorporated into UK law and what needs to change post-Brexit, click here.

Click here to view image. 

What is being published on Thursday?

The Government announced its plan for a "Great Repeal Bill" as early as the Conservative Party conference last year, with a more detailed White Paper published in March 2017. What is being published this week is the draft Bill.

Although the White Paper provided some detail on the rationale and proposed methodology behind the Repeal Bill, it left many questions open. This week, MPs will finally begin to debate the terms of the Bill itself.

What we expect is that the Bill will provide a mechanism by which the UK will give effect in domestic law to many of the same rules that apply currently via the EU.

What will be more difficult is how this will be done. The sheer volume and detail of the rules means that making sure they are all transposed in the time available – and function properly in their new domestic legal context – will be a monumental practical challenge. The process will also present political challenges, as in many cases there isn't a simple way of just "copying across" the rules – decisions need to be taken about how they work if the UK is no longer part of the EU.

Rules that currently apply across the whole of the EU – providing a basis for EU-wide standards, procedures and certifications applicable to businesses operating within EU Member States – may need to be recast once they apply only in the UK. For example, making EU law makes sense in a purely domestic context may require a new national regulator to be established to do the job previously done by an EU body or it may require references to EU bodies or other Member States to be deleted or substituted for UK bodies that already exist. This is an area in which the "devil is in the detail".

What happens next?

Once the Bill has been introduced to Parliament on Thursday, it will enter the legislative process. MPs will debate the principle of the Bill at its "Second Reading", before going on to consider possible amendments in subsequent stages of the process. If the Bill passes through the House of Commons, it will proceed to the House of Lords, where this process is repeated. The Repeal Bill must pass through both Houses of Parliament and receive Royal Assent, or it will not become law.

Although the objective the Bill is seeking to achieve is uncontroversial, the terms of the Government's Bill are likely to be a cause of controversy.

It is not difficult to see how the Repeal Bill could become a political football. The Government has suggested it will offer continuity (and so continued alignment to current EU rules). Those in Parliament who advocate a clean break from the EU could well try to find areas in which that continuity should be broken immediately; those who advocate a "soft Brexit" may argue for provisions which make it difficult to take a separate path in the future. Both sides may seek to make amendments in a Parliament in which it is not clear whether there is any clear majority for either of these points of view.

In addition, the mechanism for adopting new laws under the Repeal Bill is also likely to prove controversial. Specifically, the powers granted to Government ministers to adopt secondary legislation in order to speed up the transposition of EU law into UK law, the so-called "Henry VIII powers", and the role the Bill gives to the devolved administrations of Scotland, Wales and Northern Ireland in the process, are particular issues to look out for.

What would happen if Parliament fails to pass its Repeal Bill through Parliament?

Notwithstanding the potential controversy, legislating for Brexit is central to the success of the process. If the UK is going to withdraw from the EU in an orderly manner, the Repeal Bill, or equivalent, will be necessary to provide for the terms of the transition from a domestic legal perspective and to provide the necessary certainty for UK citizens and businesses.

Without the Repeal Bill, Brexit would be incoherent and give rise to legal chaos. Much of the rules that currently apply directly from Brussels would disappear overnight while others would no longer make legal or practical sense once the UK is no longer in the EU.

Failure to enact the Repeal Bill in some form would be highly disruptive and destabilising for the UK. For this reason, it seems likely that, however controversial, some form of Brexit legislation will pass through Parliament. The question is: how much will it resemble the draft Bill being published on Thursday?