Boris Johnson wrote in a newspaper column that seeing a “bunch of black kids” out and about set off alarm bells in his head, it has emerged.

In the old article the prime minister attacked anti-racism reforms undertaken in response to the murder of Stephen Lawrence and said Britain should “axe large chunks of the anti-racism industry”.

Written for The Guardian in 2000, Mr Johnson said in the piece that he believed he was more likely to be attacked by black youths than white youths due to press reports, did not instinctively fear the latter to the same extent, and said: “If that is racial prejudice, then I am guilty.”

The remark is just one in a series of questionable comments made by the prime minister in print. Earlier this year Mr Johnson refused to apologise for other articles he has written referring to black people as “piccaninnies” with “watermelon smiles” and calling gay people “bumboys”. He argued that his comments were “wholly satirical”.

The latest finding, which was unearthed by the Daily Mirror, saw Mr Johnson branded “fundamentally sexist and racist” by the barrister who represented the family of murdered teenager Stephen Lawrence at the Macpherson inquiry.

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Mr Johnson wrote in the column: “I am guilty none the less. Not of racism, I hope, but of spasms of incorrectitude, soon over, soon regretted.

“When I shamble round the park in my running gear late at night, and I come across that bunch of black kids, shrieking in the spooky corner by the disused gents, I would love to pretend that I don’t turn a hair.

“Somehow or other a little beeper goes off in my brain. I’m not sure what triggers it ... but I put on a pathetic turn of speed.”

Mr Johnson stated that “maybe” he would also run if it was a “gang of white kids” but said: “I’m not sure. I cannot rule out that I have suffered from a tiny fit of prejudice.”

He continued: “I have prejudged this group on the basis of press reports, possibly in right-wing newspapers, about the greater likelihood of being mugged by young black males than by any other group. And if that is racial prejudice, then I am guilty.”

He added: “And so are you, baby. So are we all. If there is anyone reading this who has never experienced the same disgraceful reflex, then – well, I just don’t believe you.”

The Macpherson reforms were set in motion by the police reaction to the murder of Stephen Lawrence (PA)

Labour candidate David Lammy, an anti-racist campaigner, said: “Stephen Lawrence’s horrific murder and the institutional racism evidenced by the Macpherson report showed beyond doubt the desperate need for anti-racism reforms.

“The fact Boris Johnson used his well-paid, privileged platform to oppose those reforms and to normalise prejudice shows beyond doubt that he is unfit to be our prime minister.

“Johnson was on the wrong side of history then, as he is now when he engages in dog-whistle racism and panders to the far right.”

Michael Mansfield QC, a crusading barrister who represented the Lawrence family at the Macpherson inquiry, told the Daily Mirror: “This is a man who is deeply prejudiced and obviously I’m horrified about the possibility that he may remain prime minister. He is fundamentally sexist and racist.

“It seems to me that this wasn’t an isolated moment of prejudice – either his observations about a ‘bunch of black kids’, or his observations about Macpherson.”

The Independent has contacted the Conservative Party for comment on this story.