According to some estimates there are more than 40,000 legal acts in the EU

Theresa May’s pledge to enshrine all EU law into British legislation to ensure a smooth Brexit is turning into a legal and technical nightmare that threatens to overwhelm Whitehall, it is claimed today.

The prime minister made the promise at the Tory party conference last month, saying that it would give businesses and workers “maximum certainty” when Britain left the European Union.

Government lawyers working on the Great Repeal Bill are understood, however, to be struggling with the complexity of the task. Experts have warned that the plan is “simply not practical”.

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Some sources are now suggesting that the bill would have to be substantially watered down or face “serious legal and practical difficulties” when it is introduced into parliament.

Lawyers from every Whitehall department