It comes as Sir Keir Starmer is facing an ongoing backlash over plans to restrict previously universal winter fuel payments to only those on pension credit, with the Scottish Government following suit.

Speaking in Edinburgh on Thursday, Mr Fanning, 73, said: “We intend to sue both the London and Scottish governments, since both are guilty through action and inaction, of damaging the welfare of pensioners.

“We are hoping to be successful, given the manifest injustice involved, however, my work as a trade unionist and shop steward has taught me that some battles are worth fighting regardless of the outcome – I believe this is one such battle.”

The judicial review – which has been raised at the Court of Session – now requires a judge’s approval to move to a hearing on the merits.

The Govan Law Centre is seeking to expedite both the case and its application for legal aid to ensure a decision can be handed down before the winter.

The case asks the court to rule on whether the decision was unlawful, which would then allow the petitioners to ask the court to, in effect, set aside the policy and restore the winter fuel payment to all.

Its argument rests on the accusation both governments failed to adequately consult with those of pension age on the change and did not release an equality impact assessment on the changes.

A freedom of information request revealed an abridged version of such an assessment had been carried out by the Department for Work and Pensions (DWP), with the UK Government arguing a full study was not required.

Former Scottish first minister and current Alba Party leader Alex Salmond put the Fannings in touch with the Govan Law Centre ahead of the action being raised.

Speaking at the press conference on Thursday, Mr Salmond said every person in Scotland “should be grateful” to the couple for raising the action.

Pointing to analysis by Labour in 2017 which suggested 4,000 people could die if the winter fuel payment was axed, Mr Salmond claimed it would be “reprehensible” for the UK Government not to undertake an equality impact assessment because such a figure would be made public.

He added: “The Scottish Government, instead of meekly accepting this, should have challenged it.

“They should have stood up for pensioners and stood up for the people as opposed to meekly toeing the line that was coming from Westminster.”

Rachel Moon, the instructing solicitor and a partner at Govan Law Centre, said: “Quite simply, (government) should have considered this rigorously.

“This policy and the decisions taken affect those with protected characteristics, including age and disability, and it affects 10 million people.”

Speaking to journalists in Holyrood on Thursday, Scottish First Minister John Swinney said he understood the “depths of concerns from members of the public”.

He added: “The hard reality that I have to face is that has been removed abruptly from our budget and we have to take action to live within the financial resources available to me.

“Because on the question of the law, I am bound by law to balance the budget and to live within the means available to the Government.”

A spokeswoman for the UK Government said: “We are committed to supporting pensioners, with millions set to see their full new state pension rise by £1,700 this Parliament through our commitment to the triple lock.

“Given the dire state of the public finances we have inherited, it’s right we target support to those who need it most.

“Over a million pensioners will still receive the winter fuel payment, while many others will also benefit from the £150 warm home discount to help with their energy bills over winter.”