“The statue of Winston Churchill in Parliament Square is a permanent reminder of his achievement in saving this country – and the whole of Europe – from a fascist and racist tyranny,” Johnson said on Friday.
“It is absurd and shameful that this national monument should today be at risk of attack by violent protesters.”
Churchill has been credited as Britain’s greatest prime minister following the defeat of Nazi Germany during World War II. However he also harboured racist attitudes towards Indians and Indigenous Australians, and his policies have been blamed for causing the Bengal famine of 1943 which killed up to three million people.
“Yes, he sometimes expressed opinions that were and are unacceptable to us today, but he was a hero, and he fully deserves his memorial,” Johnson said. “We cannot now try to edit or censor our past. We cannot pretend to have a different history.
“The statues in our cities and towns were put up by previous generations. They had different perspectives, different understandings of right and wrong. But those statues teach us about our past, with all its faults.
“To tear them down would be to lie about our history, and impoverish the education of generations to come.”
Churchill’s statue was vandalised last weekend on the same day a monument to 17th century slave trader and philanthropist Edward Colston was torn down in Bristol and thrown into the harbour.
The toppling of Colston’s statue has reinvigorated calls for the removal of other monuments to figures associated with imperialism and racism.
Authorities this week removed a statue of slave owner Robert Milligan from its plinth in London’s docklands, and campaigners in Oxford are pressing for a likeness of Victorian imperialist Cecil Rhodes to be withdrawn from view at Oxford University.
At Cambridge University, environmental protesters from Extinction Rebellion defaced a memorial window honouring geneticist and statistician Ronald Fisher, a proponent of eugenics, with the words “Eugenics is genocide. Fisher must fall.”
In Poole, southern England, authorities revised plans to remove a statue of Robert Baden-Powell to protect it from attack after supporters of the Scouts founder objected. It was boarded up instead. Baden-Powell has been accused of racism and Nazi sympathies.
Police fear new Black Lives Matter demonstrations in central London this weekend will be marred by clashes between some protesters and far-right groups which have vowed to protect prominent statues.
Tory MPs have blasted Khan for covering up the statues, but the Labour mayor said he had no choice.
“Extreme far-right groups who advocate hatred and division are planning counter-protests, which means that the risk of disorder is high,” Khan said.
“Be in no doubt these counter-protests are there to provoke violence, and their only goal is to distract and hijack this important issue.”
Johnson said he understood the “legitimate feelings of outrage at what happened in Minnesota and the legitimate desire to protest against discrimination” and acknowledged Britain had not fully combated racism and discrimination.
“But it is clear that the protests have been sadly hijacked by extremists intent on violence,” he said.
“The attacks on the police and indiscriminate acts of violence which we have witnessed over the last week are intolerable and they are abhorrent. The only responsible course of action is to stay away from these protests.”
Authorities have urged protesters not to gather because of the continued risk of spreading the coronavirus. Gatherings of more than six people are currently barred in England, though police have allowed previous demonstrations to take place.
Bevan Shields is the Europe correspondent for The Sydney Morning Herald and The Age.