Theresa May's Brexit deal risks causing a "never-ending nightmare" for British citzens and businesses, two former senior civil servants will warn today.

Lord Kerslake, former head of the Home Civil Service, and Lord Kerr, who headed up the Diplomatic Service, will say that the prime minister's withdrawal agreement would deliver a "leap in the dark" Brexit.

They will speak out as Ms May heads to Ireland for talks with taoiseach Leo Varadkar as she tries to secure fresh concessions in a bid to get her exit plan through parliament.

Launching a report by the People's Vote campaign that criticises the draft declaration on the future relationship agreed by the UK and the EU, Lord Kerslake will say the current deal would result in "an endless low-intensity political civil war".

The peer will call for Article 50 to be extended to allow for further negotiations, saying Britain is not ready for Brexit and that the "proper functioning of government" requires a deal containing more detail on the future relationship between the UK and EU.

He is expected to say: “There were once hopes, wildly exaggerated, that Brexit would be some sort of dreamland. But it is now clear it will not be an awakening for our country. Instead, it threatens to turn into a never-ending nightmare with no clarity and no closure for a decade to come.

“Brexit will become like a bad remake of Groundhog Day with the country waking each morning not to ‘I got you babe’ but the latest reports from an endless low-intensity political civil war. If – like me – you have found the last two years of political debate by turns depressing, dis-spiriting, infuriating and plain boring – the next decade will just be more and more of the same.”

Lord Kerr, formerly the UK's most senior diplomat and the author of Article 50, is expected to echo concerns about leaving the EU without more certainty about the end destination.

He will say: “To leave on the basis of Mrs May’s deal would be a leap in the dark. No-one knows where we’d end up. The next negotiation would take longer, and our hand would be weaker. The only certainty would be continuing uncertainty.”

Brexit deal vote: Opposing groups of protesters gather by parliament Show all 20 1 /20 Brexit deal vote: Opposing groups of protesters gather by parliament Brexit deal vote: Opposing groups of protesters gather by parliament Brexit supporters outside parliament PA Brexit deal vote: Opposing groups of protesters gather by parliament An anti-Brexit protester adjusts her pro-EU wig AFP/Getty Brexit deal vote: Opposing groups of protesters gather by parliament A message to Jeremy Corbyn in support of a people’s vote Getty Brexit deal vote: Opposing groups of protesters gather by parliament A mock Titanic captained by Theresa May heads towards an iceberg in a stunt by campaigning group Avaaz AP Brexit deal vote: Opposing groups of protesters gather by parliament Anti-Brexit protesters outside parliament PA Brexit deal vote: Opposing groups of protesters gather by parliament Protesters of opposing sides are in close contact outside of parliament PA Brexit deal vote: Opposing groups of protesters gather by parliament Paintings of Theresa May and Jeremy Corbyn Getty Brexit deal vote: Opposing groups of protesters gather by parliament Former Ukip leader Nigel Farage speaks to the media at the protests outside parliament Reuters Brexit deal vote: Opposing groups of protesters gather by parliament A pro-Brexit protester in Parliament Square Getty Brexit deal vote: Opposing groups of protesters gather by parliament Opposing protesters share the space outside parliament Getty Brexit deal vote: Opposing groups of protesters gather by parliament An anti-Brexit protester holds EU balloons outside parliament Reuters Brexit deal vote: Opposing groups of protesters gather by parliament Anti-Brexit protesters stand on Westminster Bridge PA Brexit deal vote: Opposing groups of protesters gather by parliament Former Ukip leader Nigel Farage speaks to the media at the protests outside parliament Reuters Brexit deal vote: Opposing groups of protesters gather by parliament Anti-Brexit protesters demonstrate outside the Houses of Parliament EPA Brexit deal vote: Opposing groups of protesters gather by parliament A pro-Brexit protester sets up outside parliament Reuters Brexit deal vote: Opposing groups of protesters gather by parliament An Avaaz campaigner holds a People’s Vote life float Reuters Brexit deal vote: Opposing groups of protesters gather by parliament A demonstrator holds a sign advocating a no-deal Brexit outside parliament AFP/Getty Brexit deal vote: Opposing groups of protesters gather by parliament An anti-Brexit protester waves an EU flag on Westminster Bridge PA Brexit deal vote: Opposing groups of protesters gather by parliament Protesters of opposing sides demonstrate outside parliament AFP/Getty Brexit deal vote: Opposing groups of protesters gather by parliament Protesters of opposing sides stand near parliament Reuters

The People's Vote report, titled "No Clarity, No Closure", criticises the lack of detail in the draft UK-EU political declaration on the future relationship.

It says the UK is yet to set out how it will guarantee the frictionless trade of goods with Europe or how it will secure a close relationship on services.