(Reuters) - British Prime Minister Boris Johnson called the granting of greater powers of self-governance to the Scottish parliament a ‘disaster’ during a call with Conservative MPs, The Sun reported on Monday.Johnson described Scottish devolution as former UK Prime Minister Tony Blair"s biggest mistake, the report here added. Scottish First Minister Nicola Sturgeon took to Twitter in response to Johnson’s reported comments. "Worth bookmarking these PM comments for the next time Tories say they"re not a threat to the powers of the Scottish Parliament - or, even more incredibly, that they support devolving more powers," her tweet here said.