The Tory peer tweeted her support for Dave after he added a surprise verse to his track “Black”, which said: “It is racist, whether or not it feels racist, the truth is our prime minister’s a real racist.”
The artist also backed the Grenfell survivors, who have alleged Mr Johnson has downgraded the importance of the disaster and is “out of touch” with what they are still going through.
Baroness Warsi – who has repeatedly criticised the failure to tackle Islamophobia in the Tory party – also pointed to the furore over the No 10 aide Andrew Sabisky, who said black people are less intelligent.
Describing Dave’s appearance as “powerful”, she said: “After the appalling appointment of #Sabisky and the shameful lack of condemnation this week from No 10 this performance felt like a necessary wake-up call in the most provocative way.”
But Ms Patel, while outlining her new hardline immigration plans, insisted “rapper Dave” simply did not understand the prime minister she knew well.
“I have worked with the prime minister for many years – he’s very much not a racist,” she told BBC Breakfast.
The home secretary said she had not watched the Brits, but said of Dave: “I don’t know how much he knows about the prime minister.”
Mr Johnson has faced repeated accusations of racism, including that he had “personally contributed” to rampant bigotry in Britain, a claim made during a TV debate last year.
He has been dogged by the articles he wrote as a journalist, including the revelation that seeing “a bunch of black kids” scared him.
During the Tory leadership race, the prime minister refused to apologise for his notorious newspaper column likening women in burqas to “bank robbers” and letterboxes”.
“He described African people as having ‘watermelon smiles’ and other disgusting smears. If that’s not racist, I don’t know what is,” the SNP Westminster leader Ian Blackford told the Commons last year.
The president of Uefa, European football’s governing body, also accused Boris Johnson of hypocrisy for criticising racism in the game given his past comments.