The bombastic Mayor of London has reportedly come under fire from a cabinet colleague after he criticised Theresa May's decision to deny the use of police water cannons in England and Wales.
A secretary of state apparently criticised Boris Johnson and claimed that the top Tory "needs to step up", The Times reported.
The attack comes after the Uxbridge and South Ruislip MP said it was "wrong" of the home secretary to veto the use of Metropolitan Police water cannons on the streets of the capital.
He argued that the three second-hand devices, which cost the force £218,000 ($338,883), would have helped the police quell the summer riots of 2011.
"The argument that was persuasive with me a few years ago was that it would be it would be wrong of politicians to withhold this utensil of crowd control from the police," he told BBC News.
The comments came after May warned that, without safeguards, the water cannons have the "capacity to cause harm".
"While evidence suggests that these water cannons are unlikely to result in serious or life-threatening injuries as currently built and used as envisaged, the assessment nonetheless poses a series of direct and indirect medical risks from their use," the home secretary told MPs.
"These include the possibility to cause primary, secondary and tertiary injuries, including musculoskeletal injuries such as spinal fracture, as well as other serious injuries such as concussion, eye injury and blunt trauma."
However, the devices are used by the Police Service of Northern Ireland (PSNI) on protestors and the Met have used the controversial crowd control devices to train with.
A Met spokesperson said: "We believed allowing police the option of deploying water cannons, even though they would be seldom seen and rarely, if ever, used, was a sensible precaution that would allow us to deal with a number of specific public disorder situations more safely and effectively than we are currently able to.
"We presented our evidence to the mayor. He supported our request, and funded the purchase of three vehicles.
"Our officers have been able to train with these for several months. This has been of significant value in developing our understanding of how to deploy the vehicles and what tactics we should adopt in the very rare event of extreme disorder.
"However, we understand that any changes to the way police are able to use force in any scenario must be very carefully considered and we know the home secretary has applied detailed scrutiny to the evidence before coming to her decision."
Meanwhile, Johnson has reportedly approached David Cameron in a bid to get the prime minister to stop his leadership rivals from "humiliating" him.
Johnson, a former member of Oxford University's elite Bullingdon Club with Cameron, apparently asked the Tory leader to "reign in" George Osborne and May, The Mail on Sunday reported.
The Mayor of London had not responded to a request for comment at the time of publication.