Boris Johnson has accused supporters of a second Brexit referendum of “doing the work of the Scottish National party” by making a second Scottish independence vote more likely and threatening the union.

In a speech in Aberdeen on Friday, the former foreign secretary and perennial Conservative leadership hopeful sought to turn the tables on remainers who argue that Brexit would increase the risk of a second independence referendum.

Announcing plans for such a vote last month, the Scottish first minister, Nicola Sturgeon, said Brexit would have such a catastrophic impact that Scottish voters must have the option to vote again, after rejecting independence in 2014.

Johnson said: “[A second independence referendum] would be nothing less than a flagrant breach of promise to the people of this entire country that when the people of Scotland voted on that matter – as they did in 2014 – with decisive effect, that verdict would be respected for a generation.

“And frankly I say to all those now campaigning for a second EU referendum in the UK – I mean Tony Blair, Alastair Campbell, and I am afraid not only John Major but even some cabinet ministers have canvassed the idea – they should know better. They are giving aid and succour to those who would stage another independence vote in Scotland.

“By undermining the verdict of the EU referendum, they are undermining the decision of 2014 and they are doing the work of the SNP and they are threatening the union. And let us be in no doubt the damage the nationalists would do. They would not only destroy the oldest and most successful political union in the world, they would destroy the very concept of Britain.”

Johnson is seen as one of the leading contenders to replace Theresa May when she steps down, as she has promised to do when a Brexit deal is passed.

One of the hurdles the Uxbridge and South Ruislip MP faces is a perception among Scottish Conservatives that his fondness for a hard Brexit and sometimes abrasive style would put off voters in the country.

Johnson was among a series of potential leadership candidates who were “discouraged” by the Scottish Tory leader, Ruth Davidson, from attending the Scottish Conservative conference in Aberdeen last weekend due to concerns their appearance could distract from her return from maternity leave.