The former head of the Vote Leave campaign has branded the Brexit Secretary as “thick as mine” and “as lazy as a toad”.
Dominic Cummings, who is also a former top advisor to Mr Gove, said David Davis’s Repeal Bill contained provisions that would allow ministers to cave in to EU demands at the last minute.
Mr Cummings’ outburst reflects continuing disagreement between different wings of the Brexit movement, which saw intense infighting at the time of last year’s EU referendum.
It comes on the same day that Mr Davis made a half day trip to Brussels to negotiate with EU officials, where he faced criticism for being pictured sitting down for talks without any notes.
In the photograph, Mr Davis’s approach was in stark contrast to the European Commission negotiators, who sat with large piles of briefing papers in organised binders.
Responding to the “thick as mince” comment, Andy Wigmore, a figure associated with the rival Leave.EU faction, labelled Mr Cummings “Super Prat”.
Mr Cummings, who masterminded the claim that Brexit could fund the NHS to the tune of £350m a week, said earlier this month that there was a chance that leaving the EU would turn out to be an “error” following a decision by “morons” in government to withdraw from the European atomic energy community Euratom.
In a stream of messages on Twitter the former Vote Leave chief said the European Union (Withdrawal) Bill tabled by the Government last week could allow ministers to alter their Brexit position at the last minute to secure a lengthy transition period, which he suggested was favoured by Mr Davis, Chancellor Philip Hammond and Cabinet Secretary Sir Jeremy Heywood.
He said the Brexit Secretary was “manufactured exactly to specification as the perfect stooge for Heywood: thick as mince, lazy as a toad and vain as Narcissus”.
Mr Cummings, a former special adviser to Michael Gove in the Department for Education, worked behind the scenes on the Vote Leave campaign which was fronted by figures including Mr Gove and Boris Johnson, while fellow Brexiteer Mr Davis appeared on platforms for the Grassroots Out organisation, which was aligned with the rival Leave.EU organisation funded by Ukip donor Arron Banks.
The Vote Leave director has now said that Mr Davis “spent the campaign boozing with (Nigel) Farage, predicting defeat and briefing (against) Vote Leave” and was involved in the “single crappest TV news for Leave of entire campaign”, when Grassroots Out unveiled George Galloway as a supporter.
Mr Cummings insisted his latest comments were not prompted by any falling out between Mr Gove and Mr Davis, insisting he had not spoken to the Environment Secretary about his Cabinet colleague since before last year’s referendum.
He said the implications of Clause 9 of the European Union (Withdrawal) Bill may not be understood by MPs or even by Prime Minister Theresa May.
The Clause gives ministers the power to use secondary legislation “to make legislative changes which they consider appropriate for the purposes of implementing the withdrawal agreement”, including by amending the Bill itself.
Mr Cummings said this would embolden EU negotiators to make greater demands on the UK because they would know ministers were not bound by the text of the bill and “can be arm twisted up to last second”.
The Government would be “empowered to ditch almost anything they promise up to last minute when arms twist”, making it much easier to implement a protracted transition period to full withdrawal from the EU, he warned.
On the photograph of Mr Davis at the negotiating table, Liberal Democrat Brexit spokesperson Tom Brake said: “We have less than twenty months of Brexit talks left, yet David Davis has skulked back to the UK after just half a day.
“He didn’t have any position papers with him because this government has no agreed Brexit position.
“This is a government with no papers, no plan and no time for the most important negotiations of a lifetime.
“They are meant to be negotiating Brexit but they can’t even negotiate among themselves.”