The UK Government has been accused of operating "under a cloak of secrecy" in its bid to thwart a legal case which could halt Brexit.

Officials have refused to release legal documents in the landmark case, prompting concerns over transparency.

The proceedings have been raised by a cross-party group of politicians who are seeking a ruling from Europe’s highest court on whether or not parliament can revoke Article 50 without the permission of other EU countries.

Scotland's top judges referred the case to the Court of Justice of the European Union (CJEU) earlier this year and just last week rejected a bid by the government to try to appeal that decision.

However, a further appeal has now been launched in the Supreme Court in London in a move which could cause significant delays to the CJEU hearing.

The Herald has attempted to access the governments legal arguments in the latest appeal, but both the Supreme Court and the Department for Exiting the European Union have refused to release the paperwork.

Jo Maugham QC, one of the petitioners in the case, said the government's refusal to release the documents was "staggering".

Mr Maugham, who has written to the Supreme Court in a bid to have the arguments made public, added: "We are satisfied that both court procedure and the principal of open justice require that the documents be released.

"We don't think a case of this constitutional importance should be argued under a cloak of secrecy and we are staggered at the government's refusal to release these documents.

"We have asked the Supreme Court for permission to make public why government says MPs must be kept in the dark about the options Parliament has if there is no deal."

The legal battle is being led by Green MSP Andy Wightman, alongside his fellow Green MSP Ross Greer, Labour MEPs Catherine Stihler, David Martin, SNP MEP Alyn Smith, Scottish LibDem MP Christine Jardine, and SNP MP Joanna Cherry QC.

LibDem MP Tom Brake and Labour MP Chris Leslie are additional parties to the action.

Ms Cherry, MP for Edinburgh South West, said that given the government is using public money to fund its case, the refusal to release the arguments constituted a "clear lack of transparency".

"We have put our arguments in the public domain, we have been upfront," she added.

"The whole process of Brexit is about the Uk Parliament taking back control, and here the government is fighting a legal case to prevent MPs from taking back control."

The politician added that given the current issues surrounding the Brexit deal, the question of whether MPs can revoke Article 50 is now "really topical" and questioned why the government was spending vast sums of money "trying to keep MPs in the dark on this point".

A UK Government spokesman said a summary of the government's submissions to the CJEU had previously been published, but documents in the Supreme Court appeal would not be released despite the government being able to do so.

When asked why the documents were being withheld, he refused to comment.

The spokesman added: "At this stage in proceedings, court documents are not in the public domain."