Sadiq Khan is facing calls to resign after his official website said a photo of a white family “doesn’t represent real Londoners”.
The London Mayor has come under fire for the message, which appeared in a branding guide on the Greater London Authority (GLA) website.
A spokesperson for Mr Khan insisted the picture caption was added “in error” and the document has now been taken down.
But critics of the Labour politician are calling on him to step down over the row.
Reform UK London mayoral candidate Howard Cox told TalkTV: “He should resign immediately. I’m sorry to say he is racist.
“I’m a white man, I’ve got a family, all white, and they are typical Londoners. I was born and bred in London. How dare he say we’re not typical Londoners.”
Reform UK leader Richard Tice added: “Resign you racist Sadiq Khan. Take some responsibility for a change.”
Former Brexit Party MEP Ben Habib added: “If anyone in office said ethnic minorities do not represent Londoners, they’d be out on their ear in five seconds flat. Sadiq Khan should resign.”
The guide included various pictures of examples of what should and should not be used while marketing Mr Khan and City Hall.
One showed a white couple and their two children out and about in the capital with the London Eye and the Palace of Westminster in the background.
The caption read: “Doesn’t represent real Londoners.”
Outspoken Tory deputy chairman Lee Anderson branded it “dog whistle politics” and urged Mr Khan to “do your job”.
Politician turned broadcaster Nigel Farage said: “Sadiq Khan’s London is run by an anti-white prejudice, which could be called racism.”
A spokesman for the Mayor of London said: “The photo caption was added by a staff member in error, and doesn’t reflect the view of the Mayor or the Greater London Authority.
“The document has now been taken off the GLA website and is being reviewed to ensure the language and guidance is appropriate.”
