On Wednesday, the Prime Minister will inform her European partners that Britain intends to leave the EU. Thereafter, negotiations will commence with these partners over the form that departure will take. This much is common knowledge. Less discussed, less understood, though no less important is the to-do list that confronts the government at home. A successful Brexit depends as much on dealing with the challenges at home as it does on the negotiations in Brussels.

I recently discussed (alongside a photo of Tim Barrow being beheaded) the kinds of administrative challenges that await. And these are about to hit home in earnest. The acid test of intra-Whitehall coordination will come when negotiations start. It seems likely that we will need to start recruiting the people necessary to make a system of customs controls work. We will also need to figure out how best to replace those regulatory functions that European institutions have carried out for us to date. What, to take but one example, will replace the EASA, Europe’s airline safety regulator, if the UK withdraws from it?

Moreover, a series of legislative hurdles must also be cleared. According to the Hansard Society, Brexit will be the biggest legislative review exercise ever undertaken by Whitehall. Much of this activity will focus around the so-called Great Repeal Bill, widely acknowledged as an almost comically misleading piece of nomenclature for a gargantuan piece of legislative incorporation.

The European Communities Act of 1972 gives domestic effect to EU legal acts. The Great Repeal Bill is expected both to repeal it, and ensure that its substance is preserved in the UK. In the words of the Department for Exiting the EU, it will transfer “existing EU law into domestic law.” This makes perfect sense, not least in that it will provide a degree of certainty about the legal framework at the point when Brexit finally occurs.

Uncertainty persists, however, about what form the Bill will take. It is hard to imagine that it will attempt definitively to list the EU legislation to be incorporated. For one thing, there is an awful lot of this, even leaving aside the significant amount that is already part of our domestic law. As one legal scholar has put it, we are talking here of issues ranging from (inter alia) external trade to competition to financial services, telecoms, fisheries, agriculture, standards agencies and the environment. For another, the precise way in which EU law will need to be incorporated into UK law will hinge crucially on the outcome of the negotiations in Brussels.

For both these reasons, it seems likely that Great Repeal Bill will allow for the liberal use of Henry VIII clauses, allowing the government to repeal or amend primary legislation by means of a secondary act. The advantage of this is clear. It will allow the government maximum flexibility to act quickly to amend or repeal legislation with minimal parliamentary oversight.

Yet this prospect has spawned serious fears. The Hansard society has voiced its concern about the increased use of Henry VIII clauses. Likewise, the House of Lords Constitutional Affairs committee has sounded a cautionary note about the implications of such powers for democratic accountability.

Above and beyond concerns about democracy, there is a concern that secondary instruments will be used to bypass parliament whilst altering the substantive content of EU laws. The government has indicated that, in areas such as customs or immigration, where significant change will be enacted, it will put forward primary legislation. But what of other sensitive areas such as trade, or the environment, or consumer rights?

The debate is already raging in Whitehall. Leaked documents suggest that parliament might need to pass a raft of additional primary legislation to cover not only immigration and customs regimes, but also tax, agriculture, fisheries, data protection, our ability to impose economic sanctions on, say Russia, EU migrant benefits, reciprocal healthcare arrangements, road freight, nuclear safeguards, emissions trading and the transfer of spending from various EU funds to individual government departments. These are all areas where simply importing existing EU laws cannot work, or where the changes proposed are too significant to be nodded through by a minister.

Here we hit the trade-off between efficiency and democratic scrutiny. Primary legislation ensures greater parliamentary involvement, but is time consuming. Even via the use of secondary legislation, ensuring a smooth transition from membership to non-membership will take time. Several of the laws to be incorporated in British law will require some degree of adaptation, if only because they reference EU institutions such as the European Court of Justice or the European Medical Agency which will cease to have jurisdiction post Brexit.

If, on top of this, there is a whole raft of new primary legislation to be passed, the scale of the task will be daunting indeed. Rumours are swirling that Number 10 has spent a lot of time trying to deter departments from insisting on standalone legislation. And it’s easy to understand why. The average Queen’s speech contains some 20 new pieces of primary legislation—and average Queen’s speeches do not have to take account of a Great Repeal Bill and a huge amount of subsequent secondary legislation. The practical strains on the system will be significant.

Moreover, each piece of primary legislation will present the House of Commons with a chance to test the robustness of the government’s slender parliamentary majority. At a minimum, the two-year timetable allowed by Article 50 (and the one year for negotiations) might start to look excessively tight.

Just because Brexit will be difficult and time consuming does not, in itself, imply that attempting it is misguided. Indeed, it could be argued that the complexity of the process to come underlines the validity of eurosceptic complaints that the EU simply interferes too much in national life.

That being said, those anxious to see Brexit work out for the best should want to be aware of, and prepared for, the challenges ahead. In purely legislative terms, they will be significant.