IT could be seen as a classic bait and switch. Theresa May’s letter triggering Article 50, we were told this week, was a historic moment. The culmination of the hopes of Ukip and Brexiters, the cause of dismay for those who wished to remain in the EU. But we knew the Prime Minister’s letter was coming, we knew (broadly) what it was going to say.

The publication of a white paper for the UK Government’s Great Repeal Bill is every bit as historic, if not more so, and just as worrying.

It sets out the government’s intentions as it seeks to extricate the UK from the legal sovereignty of Europe. It is an undertaking like no other, a near impossible task. Hence, existing EU laws will be preserved and transferred so that they continue to apply when the European Communities Act is repealed.

That process will entail what has been described as a “power grab” of extraordinary proportions, as ministers seize the opportunity to pass thousands of pieces of secondary legislation without the normal parliamentary oversight. A balance will have to be struck, as it is put in the the Bill, between speed and scrutiny.

So-called Henry VIII powers are being used – a simple necessity, the Government maintains, promising that laws passed in this way will be “time-limited”. The outcome will be the legislative freedom desired by those who voted Leave, the Government says: Our laws will be made once again in London, Edinburgh, Cardiff and Belfast, not decided by judges in Luxembourg.

But many will not initially be decided by parliaments at all. Meanwhile, the white paper appropriates additional powers to amend devolved legislation.

Nicola Sturgeon fears it will also be used to purloin powers in areas such as agriculture and fisheries which she argues should be repatriated from Brussels to Edinburgh. She is threatening to derail the legislation, and she is not alone. LibDem chief whip Tom Brake has promised to “grind the government’s agenda to a standstill” if the bill is not accompanied with rigorous safeguards.

Unlike the relatively supine approach taken by opposition parties to the triggering of Article 50 itself, there is likely to be strong resistance if the Government goes too far in the use of secondary legislation. And rightly so. The fear is that the Government will be free to dispense with long-standing protections previously founded in EU law.

Already yesterday, hard Brexiters were crowing about getting rid of “ghastly EU legislation” while others spoke of red tape. But what some call red tape, others call animal welfare, workers’ rights, or action to protect the climate. David Davis, minister for withdrawal from the European Union, says this is the beginning of a discussion between Government and Parliament about the level of scrutiny that is possible. As part of this discussion we should remember those arguing in favour of leaving the EU wanted to restore parliamentary sovereignty. It is deeply ironic that the first step of that process could involve wholesale changes to the law over which democratically-elected representatives have little or no say at all.