JACK McConnell threatened Tony Blair with Holyrood’s nuclear option in a fierce constitutional row, newly released Scottish cabinet files reveal.

The then Labour First Minister warned the Labour Prime Minister that he was ready to block a controversial Westminster Bill in case it undermined devolution.

However the files also show Mr McConnell’s concerns were brushed aside, and it was only after the House of Lords also raised the alarm that the UK Government backed down.

The row concerned the Legislative and Regulatory Reform Bill (LRRB) which the UK Government introduced in 2006, ostensibly to let ministers reduce the burden of EU-based laws through orders.

Critics said it far exceeded its remit, and would let the Governnment bypass parliament to abolish or restrict rights and freedoms, or even enact or rewrite laws at will, and it was dubbed the “Abolition of Parliament Bill”.

In Edinburgh, there was concern the LRRB could give the UK Government a short-cut to changing the 1998 Scotland Act establishing devolution and the Scottish Parliament. 

The Scottish cabinet minutes of June 21 reveal the First Minister had warned the Prime Minister the Scottish Executive would try to block the Bill by denying its devolved aspects legislative consent at Holyrood unless the Scotland Act was “made exempt” from its provisions.

Despite the unprecedented threat, no reply from Mr Blair or any UK department had been received.

The following week, Mr McConnell told cabinet he had received a reply, albeit from the then Scottish Secretary Douglas Alexander, who said the UK Government “did not intend to change its position” on explicitly protecting the Scotland Act.

The Scottish cabinet then agreed in principle to withdraw its previous legislative consent motion (LCM) supporting the Bill and bring foward its own devolved legislation.

However by August, the political tide had swung in Edinburgh’s favour.

A paper circulated to the cabinet on August 16 said the UK Government was sticking to its position in public, but “confidentially” officials had admitted this was being reconsidered.

“We understand that in light of concerns expressed in the Lords' Committee stage in July consideration is being given to options for providing express protection for constitutional statutes, including the Scotland Act. A decision is awaited from UK Ministers.

“If it is decided to protect constitutional statutes we will be advised informally (and again confidentially) but the position would not be made public unfit the amendments were tabled (in early September at the earliest). 

“If the UK Government's position changes, Cabinet will wish to reconsider the decision to withdraw the LCM and how that should be presented.

"In the meantime, no public statement has been or should be made on the Executive's position.”

In September, the UK Government finally gave in, and proposed to amend the Bill “to make clear its powers cannot be used for changes of constitutional importance”.

It was not until 2011, under an SNP Governement, that a disagreement over a Westminster Bill saw Holyrood withhold legislative consent for the first time. It led the UK Government to amend the legislation.

In 2018, Holyrood also denied consent to the main EU Withdrawal Bill key to Brexit, but Westminster pressed ahead with it regardless.