Boris Johnson, the London mayor tipped as future Conservative leader, has backed the possibility of a federal UK as he tried to laugh off the row over his "Ajockalypse Now" warning.

 

Mr Johnson said that the rise in support for the SNP meant that the entire legislative framework of the UK could have to be reconsidered.

He called for a "grown up conversation" on the issue, adding: "I'm on for that."

He also admitted that there could have to be a process of healing between Scotland and England after the General Election.

The Tory, expected to be successful in his bid to become an MP, has come under fire for his comments against a Labour-SNP alliance.

He denied that they were racist and suggested that those who thought they were were "a tiny bit hypersensitive".

He added: "In my turbulent political career there are all sorts of things I may have said or not said. This is one of the least shocking things."

On federalism, he added: "I genuinely think that after the election we need to have a sit down and people need to think about the future of Scotland.

"I want a United Kingdom but we may have to think about a federal structure for the UK. I'm on for that."

Federalism is a policy backed by the Liberal Democrats but not normally seen as traditionally Tory party territory.

However, Mr Johnson has argued in recent for more powers to be awarded to London.

David Cameron also defended Mr Johnson's comments saying: "Boris is Boris and he has a colourful way of expressing himself."

At the weekend Mr Johnson warned of the election: "It's Ajockalypse Now. People are looking at Ed Miliband and they're getting bad visuals of him popping out of Alex Salmond's sporran like a baffled baby kangaroo.

"Everybody loves the Scots.

"Nobody thinks this is going to be some tartan tyranny with everybody forced to wear kilts. But it would be a chaotic and tense arrangement.

"Labour and the SNP are like the two spent swimmers in the beginning of Macbeth.

"The sergeant says: 'As two spent swimmers that do cling together. And choke their art.' They're locked in mortal combat and the risk is they'll take us all down with them."

Mr Cameron recently named Mr Johnson as one of his potential successors in the top job.

The Prime Minister announced at the start of this election campaign that he would not stand again for a third term in 2020 if he is returned to Downing Street.

The Conservatives insist that this means he will serve a full five years and any successor will be in place only for the 2020 campaign.

But political observers have warned that for the party to be in a strong position to fight that campaign Mr Cameron would have to stand down much earlier.

That could also trigger a potentially damaging election campaign within the Conservatives.