Up to date, Boris Johnson remains the only Conservative mayor of London, following his victories in 2008 and 2012.
The Tories have shortlisted three candidates to run against Mr. Khan in 2020, including Members of the London Assembly Shaun Bailey and Andrew Boff and the first woman to be shortlisted for the Conservative party's London Mayoral Candidacy, councilor Joy Morrissey.
— Cllr Joy Morrissey (@joymorrissey) September 12, 2018
— Andrew Boff (@AndrewBoff) September 12, 2018
— Shaun Bailey AM (@ShaunBaileyUK) September 11, 2018
Conservative Party chairman Brandon Lewis praised the Tory candidates and urged them — if named the winner in September — to "take on Sadiq Khan for his failings in crime, housing and transport."
According to a YouGov poll for Queen Mary University of London, the Labour mayor saw his approval rating has slump from +22 in May this year to just +4 this month.
"In April 2018, Sadiq Khan was still ahead among those aged 50-64, working-class Londoners, those living in outer London and white voters. He's now behind among all of these groups. When we first started polling, he was one of the most popular politicians in Britain. Such was his cross-party support, he even had net positive support from Conservative voters. Those days are long gone," Philip Cowley, Professor of Politics at Queen Mary and Director of the Mile End Institute, said.
The poll has also revealed that both main parties are losing public support. Given the popularity decline of Labour and Conservatives, it remains to be seen if during the 2020 mayoral election a 'major party' candidate manages to snatch victory.
Smaller parties, on the other hand, have experienced an increase in backing.
"Support for the Liberal Democrats rose five percentage points from 10 per cent in April to 15 per cent in September. The Greens are now on five per cent, double their performance in the general election. UKIP have also doubled in support in the same time period from 2 per cent to 4 per cent," the poll showed.
Former UK Independence Party leader, Nigel Farage, announced in August he was considering running for London mayor.
Among the potential candidates of Liberal Democrats is British journalist and sister of the former London mayor, Rachel Johnson.
Despite the rise in popularity of smaller political parties, the major player candidates are more likely to assume the London mayor office in 2020.
According to a Farage ally who spoke to the Financial Times, "the three Tory candidates are so poor… no one expects any of them to win." The Conservatives may face the need to step up their game if they'd like to see Labour give up their hold on the British capital.
The next London mayoral election will be held on 7 May, 2020.