New British Prime Minister Boris Johnson has backed police powers to "stop and search" and has also pledged to provide "10,000 new places" in British prisons.

"I announce today that in all 43 police departments in England and Wales we make it clear that the police can and must use their authority to stop and search," Johnson said, according to the Mail on Sunday newspaper.

He said Finance Minister Sajid Javed had agreed to spend up to 2.5 billion pounds ($ 3.01 billion) to provide 10,000 new places in prisons.

He insisted on tougher laws for "sex offenders and serious violence", as well as those with knives.

"Yes, in the short term, this will put more pressure on our prisons, which is why I am announcing today that we will have 10,000 more places in our prisons," he said.