On the day that prime minister Theresa May formally triggered article 50 of the Lisbon treaty, legal experts have pointed out the scale of the challenge of disentangling the UK from EU law. In her letter to President Tusk beginning the Brexit process, May confirms that a white paper will be published tomorrow on legislation to convert the body of EU law, the acquis communautaire, into UK law.

Experts agreed that this will be a formidable task. Legal information specialist Thomson Reuters today said that a total of 52,741 laws have been introduced in the UK as a result of EU legislation since 1990. The government has announced that EU law-derived provisions will remain in UK law until reviewed and decisions are made as to whether to keep, amend or repeal them. However according to press reports lobbying has already begun for the repeal of some EU-derived measures, including the EU Food Information for Consumers Regulation.

Daniel Greenberg, author of Craies on Legislation, said that intense lobbying from interest groups that may suffer or benefit from the abolition of EU laws in the UK will become a major feature of withdrawal negotiations.  'So-called EU "red tape" has been central to the Brexit debate,' he said. 'Judging by the relationship of existing non-EU European countries with the EU, it is, however, unlikely we will be seeing a bonfire of these regulations.'

Much will hinge on the content of the UK’s trade agreements with the EU, he said. 'Ultimately, politicians and trade negotiators [on both sides will need to determine] exactly what the nature of the UK’s relationship with the EU will be. This, in turn, will affect the EU’s future influence over UK regulation.'

The prime minister's article 50 letter states that the government intends to bring forward 'several other pieces of legislation that address specific issues relating to our departure from the European Union' on top of the promised Great Repeal Bill. 

Thinktank the Institute for Government has reported that up to 15 new parliamentary bills will be required. In agriculture policy, for example, primary legislation will be required as leaving the EU 'will leave a policy gap that cannot be filled by mapping over existing EU laws'. 

As each Queen's speech introduces an average of 20 new bills, this will leave very little space in the parliamentary calendar for non-Brexit related legislation.

An institute paper Legislating Brexit warns that the extent of legislative change required will inevitably lead to the government resorting to different routes to make Brexit-related changes – such as using secondary legislation to amend primary legation, so-called ‘Henry VIII powers’.

Because of this, the paper argues, the government should resist the temptation to introduce non-essential changes in the repeal bill. Instead, the priority should be to copy across the acquis communautaire, which can be amended after Brexit.