A controversial poster aimed at encouraging black people to vote in the EU referendum "reinforces stereotypes", London mayor Sadiq Khan insisted.

The intervention came after Leave campaigners condemned the Saatchi and Saatchi devised image of a sari-clad Asian woman exactly balanced on a see-saw with a shaven-headed "thug" which was produced for the Operation Black Vote drive.

Mr Khan was critical of the poster, which is due to be displayed on 37 digital billboards in London and Manchester with the tag line: "A vote is a vote."

"My concern is it just reinforces stereotypes. Lots and lots of Londoners, some of my best friends who are white, don't behave that way. I've got aunties and friends who are Asian and they don't seem scared. I'm not sure what their motivation is with those particular images," Mr Khan said.

The mayor was speaking after warning a Brexit victory would be a betrayal of British values.

Addressing business people at an East London tech hub, Mr Khan said turn-out in London could decide the national poll in a knife-edge result.

Mr Khan said that both sides in the referendum campaign were guilty of overstating their case as he warned against a Leave vote.

"It would be a betrayal of real British values and send a message to the world that we wish to stand alone.

"Isolationism isnt the answer to any of the problems we face.

"We would survive outside the EU, but we would be diminished as a country, and as a city as a result," Mr Khan said.

The mayor insisted he was presenting the "patriotic, positive" case for staying in the EU.

Urging Londoners to register to vote, Mr Khan said: "A high turnout here in London where support for Remain is strongest could make all the difference."

Mr Khan again attacked US presidential hopeful Donald Trump for having "ignorant" views on Islam which played into the hands of extremists.