"I can tell you there was no impropriety as far as I'm concerned," Boris Johnson said.

British Prime Minister Boris Johnson said on Tuesday there had been no impropriety in his relationship with a U.S. businesswoman which is now subject to a possible misconduct investigation.

The government of London said on Friday it had referred Boris Johnson to Britain's police watchdog for potential investigation over allegations of misconduct involving tech entrepreneur Jennifer Arcuri while he was mayor of London.

"I can tell you there was no impropriety as far as I'm concerned," Boris Johnson said when asked about the allegations on LBC Radio.

Asked why the allegations had surfaced, he linked them to those who wanted to stop him from delivering Brexit.

"I think there's a very good reason, and that is that I've been tasked, one way or the other, to get Brexit done by Oct. 31, and there are quite a lot of well-meaning, and highly intelligent people, who basically think that would be something they don't want to see," he said.

"And I think that there is a concerted effort now to frustrate Brexit."