Sir Vince Cable has said that he worries about Boris Johnson’s politics and him “dabbling in identity politics associated with Steve Bannon” but that “it has nothing to do with his sex life”.
Mr Cable told talkRADIO’s Ross Kempsell: “I don’t want to get into his private life that is his own affair.
“People across the political spectrum have exotic private lives.
“I do worry about his politics and I think he revealed himself over the summer to be dabbling with this sort of identity politics associated with Steve Bannon.
“This rather nasty appeal to people of different religions and so on.
“I don’t like that, I think it is dangerous and it is in danger of taking over the Tory Party or the UKIP people moving in and taking it over.
“I don’t like that but it has got nothing to do with his sex life.”
This comes as Boris Johnson and his wife Marina Wheeler announced they are separated and going through a divorce after 25 years of marriage.
‘Labour has been taken over by extremists’
Watch: Vince Cable says he wants to increase support for the Lib Dems
Mr Cable announced in a speech on Friday that he would be stepping down as leader but not until “Brexit is resolved”.
Announcing his resignation in a speech on Friday, Sir Vince Cable, 75, outlined a series of reforms to membership rules aimed at attracting younger voters.
Liberal Democrat membership rules will be overhauled to all moderates outside the party to help choose the next leader, he said.
The speech comes just ahead of the party’s annual conference, which begins on September 15.
He told talkRADIO: “I would like to get to hundreds of thousands, we already have 200,000 supporters and 100,000 members.
“I would like to get that up massively so we could get a multiple of that.
"I want to create a big movement that is a rallying point for millions of people who are currently very very frustrated by the fact that the country is drifting.
“We have got the Labour Party that has already been taken over by extremists and have little prospect of reversing it.
“The Tories are being taken over by extremists as well.
“People are looking for something else and something better and more in line with moderate common sense thinking.”
‘It’s all up for grabs’
When asked about his announcements on Friday and the decision to step down when “Brexit is resolved”, he said: “People are always speculating about leader’s plans but I have made it clear that I am not standing down.
“I have got a series of very specific tasks and I think that is a professional way of doing things.
“That is the way people operated in the world I came out of before I got into politics.
“It could take a short time or a long time and I am not in control of the government’s agenda.
“It is not just getting this new movement launched but also seeing us through the Brexit process and winning the argument about the People’s Vote.
“It is all up for grabs at the moment, we don’t know what time the horizon is but I want to achieve that than set some artificial time for going.”
The Liberal Democrats have struggled electorally since going into government in coalition with the Conservatives in 2010.
As of August 2018, the party had a membership of 99,200.