Sadiq Khan was forced to distance himself from a claim on his website that a picture of a young white family “does not represent real Londoners”.
The Labour London mayor was criticised over the message, which appeared as part of a guide to his and the Greater London Authority’s (GLA) brand.
The guide opened with the words: “A City for All Londoners”, and promised to appeal to all ages, genders, sexual orientations and family make-ups.
But a picture of a couple and their two children walking along the Thames, with parliament in the background, was highlighted as an example of pictures not to use. A label on the picture read: “Doesn’t represent real Londoners”.
Mr Khan said the caption was added by a staff member “in error”, and does not reflect his view or the view of the GLA.
“The document has now been taken off the GLA website and is being reviewed to ensure the language and guidance is appropriate,” a spokesman for the mayor said.
Mr Khan’s rival in next year’s mayoral race, Tory candidate Suzan Hall, called for the mayor to apologise.
She told the Mail on Sunday, which exposed the guidance: “All Londoners are real Londoners, no matter their ethnicity, and Sadiq Khan needs to apologise and stop these desperate, politically-motivated attempts to divide people.”
The row comes as Mr Khan bids to secure a historic third term as London mayor. He has faced significant criticism in recent months over the expansion of the capital’s Ultra Low Emission Zone (Ulez), which critics say will add to the financial pressure facing households.
He has also faced criticism over the decision to charge drivers for using the Blackwall Tunnel.
Tory deputy chairman Lee Anderson last week branded Mr Khan “Dick Turpin” and a “modern-day highwayman” over the taxes.
Mr Khan’s spokesman fired back at Mr Anderson’s criticism over the Blackwall tunnel charge – pointing out that it was decided by his predecessor Boris Johnson.
“The introduction of a toll on the Blackwall Tunnel was confirmed by Boris Johnson when he was the mayor in 2012,” they said.