Lord Garnier argued supporters of the four-nation alliance were allowing SNP leader Nicola Sturgeon to “hold the floor” and so failing to make “the powerful emotional and obvious economic case for the Union”.
He dubbed Scotland’s First Minister “Glasgow’s De Valera”, after the Irish leader Eamon De Valera, who was a key figure in the fight for his country’s independence.
Lord Garnier, who has previously served as solicitor general, made his comments on Monday as peers tackled the UK Government over the delayed publication of a review of devolution led by former Scotland Office minister Lord Dunlop.
The Dunlop Review was charged with looking at how the union between the four nations could be strengthened and was commissioned by the then-prime minister Theresa May.
Speaking at Westminster, Lord Garnier said: “Will the minister agree that if we don’t make an effort Scotland will become a republic separated from the United Kingdom?”
Lord Garnier said: “Are not the unionists from every part of the United Kingdom letting Ms Sturgeon – or Glasgow’s De Valera – hold the floor because they fear confusing English nationalism with patriotic unionism and are thus failing to make the powerful emotional and obvious economic case for the union?”
Responding, Cabinet Office minister Lord True said: “I cannot conceive that anyone would wish to remove Her Majesty the Queen as our head of state.
“Everybody should advocate the United Kingdom and our union and have not fear in doing so and that goes from the lowest to the highest in the land and in every corner of our kingdom.”
Liberal Democrat peer Lord Bruce of Bennachie said: “The Prime Minister sadly shows scant understanding of or respect for devolution and yet at the same time the First Minister is obsessed with an independence referendum ahead of pandemic recovery, but has no coherent or credible plan on how to achieve it.
“Isn’t this the moment to publish the Dunlop report and set out how the UK can move forward as four nations working together?”