THE UK Government’s chief legal adviser on Scotland has launched an unprecedented attack on the country’s Law Society over its stance on Bexit.

A leaked email reveals that Lord Keen, the Advocate General for Scotland, believed a Law Society of Scotland (LSS) briefing on leaving the EU had been “political rather than legal” and not “balanced”.

MP Joanna Cherry, the SNP spokeswoman on justice and home affairs, said: “These comments are intemperate and inappropriate. The LSS has a long and respected record of impartial legal analysis."

As Advocate General, Lord Keen of Elie is a Law Officer of the Crown who advises the UK Government on Scots law.

He can also intervene on behalf of the Government in proceedings in which devolved issues have been raised.

In post since 2015, Lord Keen has now become embroiled in a row involving the LSS, the politically neutral regulatory body for Scotland’s 11,000 solicitors.

In January, following a legal bid by investment manager Gina Miller, the Supreme Court ruled that the UK Government would have to obtain parliamentary approval before starting the withdrawal process from the EU.

The Court also rejected the view that the UK Government required Holyrood’s permission to trigger Article 50.

On January 31, a senior staffer in Lord Keen’s office emailed LSS law reform director Michael Clancy and Society president Eilidh Wiseman about an “LSS briefing” on the Government legislation to kickstart the Brexit process.

The staff member wrote: “Thank you for your email of 30 January in relation to the European Union (Notification of Withdrawal) Bill. Lord Keen has asked me to convey that he has noted the terms of the communication but did not regard the comments as balanced.”

He continued: “He felt the references to the Miller case were selective and the views expressed appear to him to be political rather than legal.”

The email did not explicitly state which document Lord Keen’s office was responding to, but Clancy had earlier produced an LSS briefing on the EU notification of withdrawal bill.

In this document, Clancy outlined the position of the Society’s constitutional law subcommittee on the Holyrood dimension of Brexit: “Whilst accepting that the UK Supreme Court has come to the view that the consent of the Scottish Parliament and the devolved Assemblies is not a legal requirement before the bill is passed it should also be noted that the Supreme Court judgment is not authority for interpreting the scope of the Sewel Convention.”

The convention allows for the Scottish Parliament agreeing that Westminster may pass legislation on a devolved issue.

Clancy continued: “It might be argued that a Bill which gives the Prime Minister a power, whose exercise will inevitably alter the competences of the Scottish Ministers and Parliament, will engage the convention. For example, the triggering of Article 50 will inevitably enlarge those competences by removing the constraints upon those competences of having to observe EU law (see para 132 of the Miller decision).”

A senior legal source criticised the email: “This a blatant attempt by the Advocate General for Scotland and the UK Government to intimidate the Law Society into silence and to ensure that they think twice about saying anything that doesn't suit the UK government agenda.”

Cherry added: “The Law Society of Scotland's legal analysis of the Supreme Court's decision in respect of the Sewel Convention is accurate and shared by other impartial legal experts such as Mark Elliott, Professor of Public Law at the University of Cambridge.

“Lord Keen's email is typical of the UK government's hubris over Brexit and their desire to silence any meaningful debate or scrutiny and to rubbish intellectual criticism."

Keen, who is one of the country’s most respected lawyers, was admitted to the Faculty of Advocates in 1980 and became a QC in 1993.

Dubbed 'the Rottweiler', he defended Al Amin Khalifa Fhimah in the Lockerbie trial and represented the Henri Paul family in a case about the death of Princess Diana. He is also the former chair of the Scottish Tories.

An LSS spokesperson said: “All of our work is apolitical and impartial. We will continue to engage with both the UK and Scottish governments over the coming months.”

A spokesperson for the Office of the Advocate General said: "The Supreme Court's judgement was clear. ?We do not comment on leaked documents."