Former energy secretary Ed Davey has described London Mayor Boris Johnson as a "dangerous politician" and compared him to right-wing American presidential hopeful Donald Trump.
Sir Edward said there was a prospect that Mr Johnson could be prime minister by the end of the year, an idea he described as "troubling".
He also accused the Tories of abandoning the green agenda, not caring about climate change and making some "seriously bad decisions for our economy" around energy.
The 50-year-old, who was Liberal Democrat MP for Kingston and Surbiton for 18 years until he lost his seat at last year's general election, was knighted by the Queen at Windsor Castle on Wednesday in recognition of his political and public service.
Accompanied to the investiture ceremony by his wife Emily, brother Henry and a cousin, he described the honour as "hugely exciting".
The upside to leaving frontline politics is that "I work a lot less hard, I earn more money and I see my family", he said, but he also misses being part of the debate.
He said: "I see serious threats to Britain and indeed I find politics globally increasingly worrying as it seems to go to the extremes, and we are seeing some dangerous politicians being given air time for some dangerous views.
"We have the possibility of Donald Trump becoming the president of the United States, we have someone like Boris Johnson who could be the prime minister by the end of this year. I find these troubling."
Asked if Mr Johnson was as dangerous a threat as Mr Trump, he said: "I wouldn't say that, but he has some views which I think once they're under scrutiny rather more, people will be less inclined to support him."
Sir Edward, who since leaving politics has taken a number of private jobs linked to the energy sector, said the Conservatives are "going in the wrong direction" on energy policies.
He said: "There are many things that the Liberal Democrats achieved in the Coalition on energy and climate change that cannot be reversed.
"However those that can, and those changes for the future that Conservatives are able to make, they are all going in the wrong direction.
"Wrong in terms of prices - prices will go up because of Conservative policies - I think our energy security is more challenged now, and I think the green agenda is being forgotten."
He added: "The Tories, left to their own devices, don't seem to care about the climate and are making some seriously bad decisions for our economy with respect to energy."
Sir Edward also said he "thinks and hopes" the Hinkley Point C nuclear power station will be built, and described the European Union as "our friends".
He said: "On issues which are international which we cannot solve alone, like climate change, like security threats which might come from Russia or terrorists, by working with our friends around the table at the European Union we make British people safer."
He also said his proudest achievements as an MP were leading climate change talks with Europe and negotiations to get a strong energy security strategy in Europe following aggression from Russia.