Ministers could cling to sweeping powers allowing them to change laws without Parliament for many years after Brexit, unless Theresa May re-writes her EU withdrawal Bill.

Despite claims the far-reaching powers being granted to ministers will expire two years after Brexit, the bill’s small print allows the Government to effectively choose how long they stay in place.

The Prime Minster faces a push from Tory MPs demanding a clearer date for the termination of the “Henry VIII powers” – so called because they allow ministers to rule by proclamation.

As her Brexit team wrestles with MPs trying to reshape the bill in London, Ms May will head to Florence next week in a bid to break the deadlock in withdrawal negotiations with Brussels.

The withdrawal bill will see all EU-based regulation affecting the UK brought on to the British statute book on Brexit day – including workers’ rights and environmental protections enshrined in European law – with ministers then granted powers to alter them without the usual level of parliamentary scrutiny.

Amid concerns about ministers meddling with people’s rights, the Government accepted the need for a “sunset clause” on the powers that would see them expire two years after “exit day”.

But an examination of the bill’s text reveals ministers could name an “exit day” that begins the two-year countdown to the powers’ expiry, that is later than the actual day the UK leaves the EU – meaning the powers many not perish until three, four or even five years after Brexit depending on the day the Government names.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

Ex-attorney general Dominic Grieve told The Independent: “There’s an ambiguity in the bill as to whether the ‘exit day’ is a single date or several.

“Though the Government has never suggested anything other than a single date, it is important to clarify it.

“If it is more than one date many of the very unusual powers in this legislation would last over a much longer period.”

Mr Grieve has tabled a string of amendments to the bill including one, backed by eight other Tories, that would force the Government to confirm that all of the exit days referred to in the legislation are the same date.

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Among other Conservative backers are ex-cabinet minister Nicky Morgan, who said: “It’s clear MPs are already concerned about the extensive Henry VIII powers.

“To have different exit days, and the powers falling away over a different period that could last several years longer than expected adds to that uncertainty.”

Another former Conservative minister who has put his name to the “exit days” amendment, Stephen Hammond, told The Independent: “The bill as set does allow the Government to choose different ‘exit days’ for different parts of the legislation.

“They need to clarify why it’s worded in that way, and if there’s no good reason then there should be one ‘exit’ day’.”

A spokesman from the Department for Exiting the EU said: “Exit day will be the day we leave the EU - and that will be set out in law.

"The powers in the Bill are time limited after exit day and will be used to ensure that our statute book continues to function after exit.

"As Ministers have made clear, we will look with the utmost seriousness at the amendments that are tabled."

Overall, more than 150 amendments have been tabled to the withdrawal bill from MPs from different parties, covering almost 60 pages, with many focussing on the Henry VIII powers.

Other changes focus on Parliament having a final say on any Brexit deal, on the Commons controlling the length and terms of a transition period and on protecting rights enshrined in EU law.

Ms May will travel to Florence on Friday to make a major speech on Brexit, in a bid to kick-start stalled talks with the EU.

She is expected to give European dignitaries her view on the state of Brexit talks and “assist” her negotiating team in nudging discussion on to critical future trading relations.