MINISTERS feared arch Unionists would try and scupper Scottish devolution by mounting a legal challenge ahead of the 1997 vote, secret papers reveal.

Files obtained by The National after a two-year freedom of information battle with the Conservative Government, which opposed their release, show that the Cabinet were anxious to forestall any threats which could derail the vote and the re-establishment of the Scottish Parliament.

No individual or specific group is mentioned in the papers as planning a legal challenge, but the letters and documents made public for the first time show the Labour government was sufficiently concerned to set up a working group on the matter and ensuring lawyers vetted all pro-devolution publicity material.

The SNP, Labour, the LibDems and Scottish Greens all campaigned for a “Yes” vote for a Scottish Parliament and that it should have tax varying powers, while the Conservatives opposed both proposals.

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The Scotland Office files are marked “restricted” and are held by the National Archive of Scotland in Edinburgh.

A note, dated July 9, 1997, drawn up by the Cabinet Office’s Constitution Secretary, warned leaflets sent out to households were vulnerable to be seized on by opponents to mount a legal fight.

“Any decision by the Government to distribute information during the referendum campaign will be vulnerable to challenge by way of judicial review,” it said.

“The challenge would probably be mounted on the basis that no reasonable Secretary of State could have reached the decision to distribute such information. The applicants might allege, for instance, that the information provided was one sided or that it failed to accurately represent the argument against devolution.”

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On July 15, 1997, minister without portfolio Peter Mandelson wrote to the Lord Chancellor Derry Irvine to say that as a result of the legal threat all publicity material would be checked by lawyers.

“We have to be careful. Even a failed challenge could cause delay if disruption of publicity has to be suspended while the case is heard,” he wrote. “And a challenge could divert attention from the devolution debate itself.”

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He added: “It will be necessary to ensure ... that all publicity materials are vetted by lawyers.”

As revealed by the Sunday National yesterday the Scotland Office sought to deny public access for more than two years to the secret 1997 files in part on the grounds they could damage relations between Edinburgh and London amid the independence debate.

The National: Alister JackAlister Jack’s officials finally agreed to open the documents after dropping a legal appeal last month against a ruling from the information watchdog that some of the paper must be released.

Contained within the papers handed to The National is a letter from Tony Blair to William Hague after the Tory opposition leader wrote to him asking for the referendum not to take place on September 11, 1997, citing Princess Diana’s death.

The papers’ release comes amid the continuing constitutional debate in Scotland with more than 20 successive polls recording majority support for independence.

It also follows a repeated refusal by the Conservative Government to agree to a second referendum, with Boris Johnson suggesting a new vote should not take place until 2055 and describing devolution as “a disaster north of the Border” and “Tony Blair’s biggest mistake”.

The process of getting hold of the files dates back to November 2018 when The National submitted a freedom of information request to the Scotland Office requesting six files relating to the 1997 referendum.

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Public bodies normally have 20 days to give a response and the Scotland Office made two extensions to the request before rejecting it on February 7, 2019.

In July last year, the UK’s Information Commissioner ruled some of the files must be opened. However, the Scotland Office lodged an appeal against the watchdog’s decision. It dropped its appeal last month and the files were made available.

The National: SNP MP Mhairi Black addresses her party's National conference in Aberdeen in October

Mhairi Black, the SNP’s shadow Scotland Office spokesperson, said: “Fast forward from 1997 and the opponents of devolution today are ramping up efforts to actively undermine it at every opportunity. With Boris Johnson previously stating devolution has been a ‘disaster’, it’s clear that Scotland’s interests are under threat from Westminster.

“The reality is Scotland has been hit with years of harmful Tory policies and austerity, and we have been left to tackle this pandemic with one hand tied behind our back as Westminster withholds funding and the devolution of powers. It’s clear beyond any doubt that only with independence can we properly protect our interests and get on with building a fairer and more equal society.”

Former first minister Henry McLeish said: “It has taken an extraordinary length of time to get [the papers] and the reply given ... suggests very fragile relations between the UK and Scottish governments.”

A UK Government spokesperson said: “The Office of the Secretary of State for Scotland handles all freedom of information requests strictly in accordance with the relevant legislation, and this includes the appeals process.”