At least half of voters think they would be just as good or better at running the capital than either Mr Khan or his two predecessors in City Hall — Ken Livingstone and current Prime Minister Boris Johnson.
Some 36 per cent of those polled said they could outperform Mr Khan, while a further 23 per cent think they could do just as well.
Only around one in five (18 per cent) people felt the Labour mayor, who was elected in 2016, was doing better in the role than they could do themselves.
For Mr Johnson, who served as Conservative mayor between 2008 and 2016, some 41 per cent said they could do a better job, while 20 per cent thought they could do just as well.
As with Mr Khan, just 18 per cent of respondents thought they would make a worse mayor.
Asked to recall Mr Livingstone’s stint as London’s first mayor between 2000 and 2008, respondents were less sure about their ability to outperform the left-wing firebrand.
A more modest 32 per cent said they could have done a better job, and significantly more were unsure about how they would fare against Mr Livingstone compared to the two most recent mayors.
Connor Ibbetson, a data journalist at YouGov, said: “These results do break down on political lines, with more Tory voters than Labour ones thinking they could do a much or somewhat better job than Sadiq Khan and Ken Livingstone, while the inverse is true when asked about Boris Johnson.”
The polling also revealed that a significant proportion of voters from each mayor’s own party think that they could outperform them.
For Mr Khan, 36 per cent of London Labour voters think they could do better, while 32 per cent of Tories in the capital claim they could outdo Mr Johnson as mayor.
And for Mr Livingstone, who served his first term as an independent and his second as Labour, almost a third (31 per cent) of Labour-voting Londoners said they could do better.
A recent poll by Redfield and Wilton Strategies has the current mayor, Mr Khan, well ahead and predicted to take 51 per cent of first preference votes, ahead of his Tory rival Shaun Bailey on 25 per cent.