PM is said to have told northern Conservative MPs he believed the way powers had been handed to Scotland was “Tony Blair’s biggest mistake”

The controversy represents the latest clash between Mr Johnson and Mr Ross, who has criticised the Governments approach to Scotland several times since taking over from Jackson Carlaw earlier this year. 
Speaking shortly after his election in October, Mr Ross told delegates at the Conservative Partys virtual annual conference:  “Many, including some who govern our country, want to see a UK Government focused on England.”
On Monday evening a No 10 source said: The PM has always supported devolution but Tony Blair failed to foresee the rise of separatists in Scotland. 
“And leaving the EU means we must strengthen and protect the UK economy with the UKIM Bill.
“Devolution is great but not when its used by separatists and nationalists to break up the UK.
Shadow Scottish secretary Ian Murray criticised Mr Johnson’s remarks as he defended devolution as “one of Labour’s proudest achievements”.
“This confirms that Boris Johnson doesn’t believe in devolution and would put the future of the United Kingdom at risk,” the Labour MP said.
“His Government should have been working in partnership with the devolved governments during this crisis. Instead, people across the UK have been paying the price for his failings.”