The UK's government flagship Brexit law is "hopelessly misleading" and is nothing more than a "distraction" for MPs, a top constitutional law expert has warned.

University of Cambridge's Professor Mark Elliott said the Great Repeal Bill, which is designed to scrap the European Communities Act 1972 and enshrine all EU law into UK law, will be "legally irrelevant".

"By the time the UK exits the EU, it will by definition have ceased to have relevant Treaty obligations, and the ECA will therefore not give effect in the UK to any EU law anyway," Elliott said, writing in his Public Law for Everyone blog.

"Meanwhile, far from repealing EU law, the Great Repeal Bill will in fact preserve all EU law (or at least all the EU law whose retention makes sense once the UK has left the EU) by converting it into UK law."

The comments were made in reaction to David Davis' statement to the House of Commons yesterday. The Brexit secretary also reconfirmed that the government would not give parliament a say on the triggering of Article 50, the official mechanism to split from the EU.

Former Labour leader Ed Miliband, among others, have called for MPs to have a vote on the issue. Elliott, who advises the House of Lords' Constitutional Committee, said the Great Repeal Bill appears to be an attempted "distraction" away from the Article 50 issue.

"The intention, it might be inferred, is to placate parliament by seeking to convince it that it is being offered a meaningful role in the Brexit process," he said.

The government will be forced to defend its stance in England's High Court from Thursday (13 October). Attorney General Jeremy Wright QC MP, James Eadie QC, Jason Coppel QC, Tom Cross and Christopher Knight will ask the court to reject a challenge.

"The country voted to leave the European Union, in a referendum approved by Act of Parliament," Wright said.

"There must be no attempts to remain inside the EU, no attempts to rejoin it through the back door, and no second referendum. We do not believe this case has legal merit. The result should be respected and the government intends to do just that."

Prime Minister Theresa May has promised to trigger Article 50 by March 2017, which is expected to be followed by at least two years of negotiations with Brussels.