Ms Lawrence, who does not normally become involved in party politics, said she had been moved to make the criticisms by her anger at Mr Johnson's attitude to the Macpherson inquiry in 1999 into the Metropolitan police's failure to bring her son's killers to justice 14 years ago.
Ms Lawrence said: "Boris Johnson is not an appropriate person to run a multi-cultural city like London. Think of London, the richness of London, and having someone like him as mayor would destroy the city's unity. He is definitely not the right person to even be thinking to put his name forward.
"Those people that think he is a lovable rogue need to take a good look at themselves, and look at him. I just find his remarks very offensive. I think once people read his views, there is no way he is going to get the support of any people in the black community."Mr Johnson wrote a series of articles at the time of the Macpherson inquiry, claiming some of its recommendations were born of political correctness and that the furore around the murder had created the whiff of a witchhunt against the police. The inquiry team found the police institutionally racist.