The Prime Minister’s right-hand man attacked the justice system during a discussion about crime policy last week. Mr Cummings insisted too many foreign criminals who commit serious offences in Britain are not deported or end up returning.
He also warned the public thinks politicians are “crazy” for failing to take a tougher stance, the Mail on Sunday reported.
Mr Johnson’s top aide said: “The whole thing is absolutely f****** mad and we’re going to change it.”
About 12 percent of the prison population is thought to be from overseas.
Mr Johnson appointed Mr Cummings, who ran Vote Leave during the Brexit campaign, as his special adviser following his move to No 10.
He was recently played by Benedict Cumberbatch in a film about the 2016 referendum called Brexit: The Uncivil War.
And Mr Cummings was previously a special adviser to Michael Gove.
Speaking to Sky News earlier this week, Mr Cummings said preparations for leaving the EU with no deal on October 31 were going “great”.
He added: “The most simple thing is the Prime Minister believes that politicians don’t get to choose which votes they respect, that is the critical issue.”
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Writing in the Mail on Sunday, he said: “In the past five years, we have seen literally hundreds of convicted rapists who have come out of prison commit another sexual offence.
“This cannot go on. I am afraid that as a society we have no choice but to insist on tougher sentencing laws for serious sexual and violent offenders, and for those who carry knives.
“Our first duty is to protect the public in the most basic way – and that means taking such people off the streets.”
Mr Johnson added the “first duty” of any Government was to protect the public.
He said: “We have the impression of a growing culture of insolence on the part of the thugs; and in the face of that sense of impunity – entirely misplaced – I believe the British public knows instinctively what we must do.
“We need to come down hard on crime. That means coming down hard on criminals.