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Labour vowed to try and block Theresa May's Brexit “power-grab” when MPs vote on her flagship repeal Bill .

Jeremy Corbyn will order his MPs to oppose Tory plans for quitting the EU by dodging parliamentary scrutiny under “Henry VIII powers”.

The showdown will provide a test for Mrs May's authority at a crunch Commons vote on Monday night.

A Labour spokesman said: “As democrats we cannot vote for a Bill that unamended would let Government ministers grab powers from Parliament to slash people’s rights at work and reduce protection for consumers and the environment.

(Image: AFP)

"Parliament has already voted to leave the European Union. But the Government’s EU Withdrawal Bill would allow Conservative ministers to set vital terms on a whim, including of Britain’s exit payment, without democratic scrutiny.

"Nobody voted in last year’s referendum to give this Conservative government sweeping powers to change laws by the back door. The slogan of the Leave campaign was about people taking back control and restoring powers to parliament.

"This power-grab Bill would do the opposite.”

Tory Remainers have signalled they could rebel over the legislation in later stages and bristled at suggestions from party whips that doing so would amount to supporting Labour.

Brexit Secretary David Davis will face a grilling from MPs as Parliament returns from its summer break.

It follows months of negotiations which EU leaders complain have failed to deliver “decisive” progress on key issues.