Sir Menzies Campbell warned Boris Johnson that he must now wake up to the “real world” following his election success.

The LibDem peer also cautioned the public that they have yet to see the “true” Johnson and that the only difference between him and Donald Trump was the fact Johnson can speak Latin.

Speaking to The Herald on Sunday, Campbell said the new Prime Minister had hidden during the General Election campaign and, with him having been subject to barely any scrutiny, the public were yet to see his true colours.

He said: “Johnson – he’s just like Trump. Today they would tell you it was white and tomorrow they would tell you it’s black, and it wouldn’t matter if they were telling you the truth or not.

“The inadequacies that we all know about are much more likely to be exposed now, seeing as they were hidden in that carefully constructed campaign in the General Election.

“They managed to hide Johnson during the campaign. They gave him a series of silly photo opportunities but they kept him away from the big beasts like Andrew Neil, and from real scrutiny.

“He’s only done about two Prime Minister’s Questions by now, but he cannot hide any more. Welcome to the real world, Mr Prime Minister.”

Campbell said the public can expect to see more gaffes from Johnson like those seen during the election campaign and explained: “He is a man whose mouth engages before his brain. Look out for the same kind of faux pas in relation to that quite bizarre and extraordinary episode where he took the phone off the reporter, and he never quite explained what that was.

“This is a man who is as unpredictable as Trump in many respects … even if he does speak Latin quite well. That’s the only difference between them.”

On his own party’s leader during the campaign, Campbell said Jo Swinson was a “phenomenal” leader who was subjected to a huge amount of scrutiny that a male counterpart would never have been.

Swinson, who was elected to the House of Commons at the age of 25, becoming the youngest MP in history, stepped down almost instantly after she lost her own East Dunbartonshire seat to the SNP’s Amy Callaghan on Thursday night.

Some senior party members said Swinson’s downfall came from her declaration that she was a candidate to be Prime Minister as well as the key focus of the LibDems’ campaign being to cancel Brexit and revoke Article 50.

The 39-year-old was the first woman to lead the LibDems and came under fire from opposition politicians and from the public, who criticised her accent, how she looked and the fact her family was based in London.

Many members of her own party and political commentators said she had been subject to gender-based scrutiny.

Campbell said: “Among the faithful there was no doubt she was well liked, admired.

“Nobody worked harder than Jo Swinson, but Jo has been the subject of misogynist comment. Just imagine what any woman leader would have to put up with if she had the same personal history as Boris Johnson.

“The photograph of Sturgeon cheering will follow her for a long time. What became of gracious in defeat and magnanimous in victory?”

On the subject of his own party, which is now leaderless, the former MP for North East Fife said it had the chance to be an effective centrist opposition while Labour leaned more to the left, and the Tories more to the right, if it managed to get its message and policies right.

He said: “Where do we go from here? I think that Ed Davey, he was used increasingly in the campaign towards the end and he would be an obvious choice for leader as he is currently deputy. He was in the Cabinet too.

“I don’t know whether he would be willing to do it – I haven’t spoken to him, and he went through a leadership contest recently.

“Anything he did in the course of the election campaign was wholly competent. We need a bit of stability and he is certainly capable of that.

“Whoever it is, the LibDems need a steady hand, self-discipline and coherent policies to counter what we can expect from a Boris Johnson administration and a Labour opposition.

“The gap will open up and we have to be ready to take advantage of it. We need to export the kind of enthusiasm and expertise that served us so well in North East Fife.”

The constituency, which was the most marginal in the UK with a majority of two, has been hailed as a great win for the LibDems.

Nicola Sturgeon visited the area several times throughout the campaign, with the SNP pulling out all the stops to ensure they kept a hold of the area.

Despite their efforts, it swung back to the LibDems, with Wendy Chamberlain becoming the new MP for the constituency, defeating the SNP’s Stephen Gethins.

Chamberlain gained 19,763 votes compared to Gethins’ 18,447, giving her a majority of 1,316.

The result flew in the face of an exit poll that predicted a win for the Nationalists.

Chamberlain is one of several newer female members of the LibDems to have succeeded this year, with others including Munira Wilson, who secured Vince Cable’s old seat of Twickenham, and Daisy Cooper, who won the St Albans constituency from Anne Main of the Conservatives.

Campbell said: “The Nats threw absolutely everything but the kitchen sink at Wendy’s seat in North East Fife.

“I don’t know how many times Sturgeon came – she even came and made a major speech of her campaign there.

“When they threw everything at the contest in order to preserve Stephen Gethins’ position, it shows that if you have an outstanding candidate, good local support and great organisation then you can withstand the nationalist juggernaut in Scotland.”