Theresa May’s plan to “rig” Parliament to prepare for Brexit was hatched immediately after her general election disaster but kept secret, The Independent has learned.

The Democratic Unionist Party (DUP) agreed to help the Conservatives seize control of all Commons committees – despite losing their majority – when it struck the June deal to prop the Tories up in power.

However, that crucial part of the deal, paving the way for ministers to force through up to 1,000 “corrections” to EU law ahead of Brexit, was not mentioned in the so-called “cash-for-votes” agreement.

Instead, control of committees will be secured in a late-night vote next Tuesday, when the DUP will back the Prime Minister – although it has refused to confirm that support publicly.

“It was all decided in discussions between the Conservative and DUP whips immediately after the election result,” a well-placed source told The Independent.

“Don’t forget those whips worked hand-in-hand through the Cameron and May mark one governments. So they were always going to in May mark two as well.”

Tuesday’s motion – revealed by The Independent – provoked a fierce backlash yesterday. Jeremy Corbyn described it as “an unprecedented attempt to rig Parliament and grab power” by the Conservatives.

The SNP said the Prime Minister was guilty of “daylight democratic robbery as it seeks to defy the result of the general election”.

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And the Liberal Democrats vowed to try to amend the motion to block a blatant attempt to “rig parliamentary committees and ram through the Government’s hard Brexit plans”.

“Eroding democratic institutions and rigging the rules in your favour is something we’d expect from a banana republic, not a Conservative government,” said Vince Cable, the Lib Dem leader.

No 10 was thrown on the defensive, insisting it had a right to majorities on all committees because it had a “majority” in the Commons itself.

That argument prompted allegations that Ms May was trying to rewrite the June result, refusing to recognise that the voters had removed her power to govern alone.

Tuesday’s motion will seek to rip up Commons rules so that “the Government shall have a majority” on committees and on the body making nominations to them, despite relying on the DUP deal for power.

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Parliamentary officials had advised the Tories were not entitled to that majority, but the party will push the controversy to a vote after attempts to reach a private deal with opposition parties broke down.

Without the fix, it would be impossible to force through the vast amount of delegated legislation planned to “correct” EU law in preparation for Brexit, which has triggered accusations of a power grab.

Some changes will be made using “Henry VIII powers”, so-called because they date back to a 1539 law allowing the Tudor monarch to govern by proclamation, without consulting MPs.

Publicly, the DUP agreed to back the Conservatives only on finance bills, Brexit legislation and protecting “national security”.

But control of committees will also allow the Government to press ahead with other legislation where support is due to be decided on a “case-by-case basis”.

Ms May’s spokesperson described the motion as “common sense”, warning the Commons chamber would otherwise become bogged down in many hours of passing detailed, technical legislation, creating a logjam.

“The effect of this would be unacceptable delays, when the public has an expectation for the Government to deliver business through the House in a timely fashion,” she said.

She also said: “The Government has a majority on the floor of the House, therefore it’s perfectly legitimate that it puts to the House, and therefore MPs, that it should also have a majority in committees.”

The spokesperson directed detailed questions about the extent of the agreement with the DUP to the Tories’ Commons Leader’s office, but The Independent’s calls were not returned.