"I have paid the fine and I once again offer a full apology," he said in a video posted online by Sky News.

He argued it did not occur to him that he was breaking the law when he attended a "brief gathering" in the cabinet room at Downing Street in June 2020 to mark his birthday.

"In all frankness, at that time it did not occur to me that this might have been a breach of the rules, but, of course, police have found otherwise," he said.

Johnson added that the best thing he could do now was to "focus on the job at hand." He said he would not resign.

He has faced growing calls to step down from both the opposition and his Conservative party.

(With UNI/Sputnik inputs)