A former Tory MP has condemned the "appalling choice" voters face between Boris Johnson and Jeremy Corbyn.
In a scathing attack in the Evening Standard, Nick Boles accused Mr Johnson of being a "compulsive liar" and called Mr Corbyn a "totalitarian".
Mr Boles - who quit the Tories over their stance on Brexit - also revealed he would vote Liberal Democrat.
He said it would "not entail the kind of moral compromise" of voting Tory or Labour in 12 December's election.
BBC News has contacted the Conservatives and Labour for a response.
Mr Boles urged people to vote for "whichever party is best-placed to challenge" the two largest parties in Westminster.
Last week, former Labour MP Ian Austin said he would be voting Conservative as Mr Corbyn was "completely unfit to lead our country".
In his article, Mr Boles said the 12 December poll would be "the only election in modern times in which you wouldn't trust either of the prime ministerial candidates to mind your children for an hour, let alone run the country".
The former MP, who used to work for Mr Johnson when he was Mayor of London, made a number of personal attacks about his old boss' honesty.
He also accused the PM of "turning the party of Disraeli and Churchill into a vehicle for shrill English nationalism", and said Mr Johnson had "purged its ranks of anyone who favours a close relationship with our European partners".
Turning his fire on Mr Corbyn, Mr Boles said: "Like all leaders of a totalitarian mindset, he is entirely uninterested in the lives of individual human beings.
"He cares only for classes and factions, and the struggle between abstract political forces."
Mr Boles said voters "will not remake Britain's political system in one day", but could make a start by voting for his former political rivals, the Liberal Democrats.
"I will vote for Jo Swinson's candidate because it will not entail the kind of moral compromise that voting Conservative or Labour would," he added.
"I trust her to pursue the closest possible relationship with the European Union after Brexit.
"And, most of all, because the Liberal Democrats will insist on electoral reform and the introduction of a proportional voting system, which is essential if we are ever to break free of the tyranny of the two big parties and open up British politics to new forces, new faces and new ideas."
Mr Boles was part of a cross-party group of MPs who tried to find a compromise in Parliament back in March around a Brexit proposal that would retain access to the single market.
After his "Common Market 2.0" plan was rejected by MPs for the second time, he accused his party of "failing to compromise", saying he could no longer represent them in the Commons and would sit as an independent.
He has decided not to stand at the upcoming election.