The Government is facing the prospect of crucial Brexit legislation being held up by the House of Lords after the Liberal Democrats threatened to force hundreds of votes on far-reaching legal changes.

Opponents said ministers have not left enough time for the changes to be properly scrutinised by Parliament, and warned it is now “logistically impossible” to pass all the legislation needed to avoid legal confusion after Brexit.

Senior Liberal Democrat sources told The Independent the party’s peers will probably try to call debates or votes on “at least half” of the 800-1,000 changes to EU statutes the Government says are needed in order to transfer them into British law before Brexit – potentially taking up weeks of parliamentary time.

Some of the legal “corrections” relate to crucial issues like the regulation of medicines, nuclear materials and aviation, meaning failure to enact them by next March could have significant consequences. Others are needed to clarify which bodies will uphold laws that were previously overseen by EU courts.

Opposition MPs claimed it would be “logistically impossible” for all the legislation to be implemented in time, unless the Government cancels MPs’ holidays.

Vince Cable, leader of the Liberal Democrats, said: “It looks logistically impossible for the Conservatives to get the statutory instruments resulting from their EU (Withdrawal) Bill through Parliament before their preferred Brexit date of March next year.

“The only way they would have a fighting chance would be to cancel Christmas and summer holidays for MPs. That might upset their backbenchers, but we’ll oppose their shambolic Brexit wherever, whenever.

“Even if the Conservatives attempt to get this done in time, it will mean swathes of bills in other key areas would have to be dumped, which is not good for the country.”

Ministers say the process of tabling the changes will begin as soon as the EU (Withdrawal) Bill is passed, most probably in June.

That gives the Government just seven months of parliamentary time to make the 800 to 1,000 regulatory changes that have been deemed a necessity before the UK leaves the EU.

Around 1,200 such “statutory instruments” have been passed by Parliament in each of the last two years. With the Brexit changes on top, MPs and peers would have to get through double that number in little more than half the time.

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While agreeing a transition period with the EU could give ministers more time to make the changes, government sources told The Independent they are pushing ahead with plans to enact all of the changes by next March, because such a period is yet to be agreed with Brussels.

Most of the statutory instruments will be discussed in committees rather than by the entire House of Lords, but the threat of hundreds of debates is likely to cause ministers a headache as they begin the arduous process of amending existing UK law to make Brexit a reality.

Commenting on plans to oppose hundreds of the statutory instruments in order to force them to be debated in the Lords, a Lib Dem source said: “This isn’t about holding up Brexit – it’s about making sure these changes are being properly scrutinised. It’s the Government’s responsibility to leave enough time to get this through.”

The EU (Withdrawal) Bill, currently before Parliament, gives ministers the power to use statutory instruments to make the legal changes needed to enact Brexit.

Statutory instruments are classed as either affirmative, meaning they require a vote of both Houses of Parliament, or negative, in which case they are approved by default after 40 days unless a peer or group of MPs request a debate or force a vote on the matter.

What is the Brexit 'transition'?

If Lib Dem lords push ahead with the strategy, hundreds of hours of parliamentary time could be taken up as committees of peers pore over and debate the proposed changes.

A Brexit Department spokesperson warned: “The purpose of the EU (Withdrawal) Bill is to provide a functioning statute book on the day we leave the EU.

“If the majority of statutory instruments do not complete their parliamentary process before exit, there will be gaps in domestic law.”

A report by the Brexit Select Committee late last year concluded that passing the 800-1,000 changes before next March was an “absolute necessity”.

But it warned: “It remains the case that uncertainty will only be removed if all the necessary legislative amendments are in place by exit day to ensure that there are no gaps left in the statute book.

“This will require substantial parliamentary time and we believe that this must be found even if it results in longer sitting hours or a curtailed parliamentary recess.”

Among changes that need to be passed are laws that relate to EU institutions that the UK may no longer be part of after Brexit.

For example, the law currently states that British medicines are regulated by the European Medicines Agency, but there is no guarantee the UK will remain a member of this organisation beyond next March. Failure to amend the legislation to appoint a new regulator before then raises the risk of medicines being inadequately regulated after Brexit.