Martin Howe QC said some MPs wrongly believe Parliament could pass an amendment which would allow Britain to quit the backstop arrangement. The legal expert warned the terms of Mrs May’s deal clearly state that Brussels has the final say over when the UK can leave – and a “parliamentary lock” over whether to enter the arrangement would be nothing more than a “mirage”. Mr Howe said claims by Mrs May that the UK has a “choice” over whether to enter the backstop are misleading.
In a damning criticism of the Government’s approach, he said the Prime Minister’s “desperation” to pass her Brexit deal has led to Downing Street straying “beyond the realms of normal political spin and exaggeration into the territory of relying on misrepresentation of the legal consequences”.
And he said the only real choice over the backstop that MPs have is the decision over whether to accept or reject the deal.
The Prime Minister has spent the week desperately attempting to secure reassurances from the EU over the Irish backstop terms set out in her Brexit deal.
The arrangement would see the whole UK remain in the bloc’s customs union to avoid a hard border in Ireland.
But Tory Brexiteers fear the terms would trap Britain in the deal indefinitely.
In a bid to ally their concerns, Mrs May has repeatedly insisted the backstop is just a contingency which neither the UK or EU wants to use.
And in a string of meetings with European leaders this week, the Prime Minister attempted to ally the fears of her Eurosceptic backbenchers by securing assurances that the backstop would not trap the UK for years to come.
But legal advice already published by the Government said the terms of the Brexit deal could require “protracted and repeated rounds of negotiations” to leave the arrangement.
The advice also warned the backstop would “endure indefinitely” until a new arrangement takes its place.
Writing on the Brexit Central site, Mr Howe said: “Despite the clarity of the advice, some Members of Parliament seem to be convincing themselves – or maybe are being convinced by others – that there could be other routes out of the backstop if only the right amendment is framed in Parliament.
“It is vital that Parliament should not vote based on a mistaken understanding or wishful thinking about the legal situation.”
The Irish border backstop would kick in if the UK and EU are unable to agree trade terms which avoid the need for customs checks by the time the proposed transition period comes to an end, currently in December 2020.
Mr Howe explained that the UK could get out of the arrangement through arbitration with the EU.
But he pointed out the Government’s own legal advice had warned that Brussels would be under no obligation to propose new terms which the UK would find acceptable.
Instead, the EU would only have to show “good faith” – which would only require the consideration of Britain’s proposals, not necessarily the acceptance of them.
Mr Howe said: “So the Government and Party machines have been pushing in public legal arguments which the Government’s internal advice reveals they know to be rubbish.
“It is regrettable that Theresa May’s desperate political struggle to sell her deal to a sceptical Parliament, party and country has gone beyond the realms of normal political spin and exaggeration into the territory of relying on misrepresentation of the legal consequences of the deal.”
On the possibility of a “parliamentary lock” for the backstop, which would allow MPs to vote before the deal kicks in, Mr Howe warned such an agreement would not allow the Commons to block it.
Because the backstop would be part of an international treaty, it would kick in regardless of whether Parliament voted for it or not, Mr Howe said.
Ministers said this week that a new vote on whatever revised terms Mrs May secures with Europe will take place no later than January 21.