Stanley Johnson was snapped flouting mask rules in Greece just days before he did the same in England.
The Prime Minister's dad was spotted in an airport in Athens last Sunday (27 September) with his mask pulled down to his chin while he read a book.
According to Greek rules, face masks must be worn at all times in public spaces - such as busy airports.
Johnson, 80, was on his way home to the UK after a three-week holiday at his villa in Greece when he was seen, the Daily Star reports.
A police source told the newspaper: "It does not matter who you are, celebrity or no. We are all doing our best to stop the virus spreading, and we will be very hard on those who do not listen.
"You must wear a mask, and if you don't we will give a big fine. He should be warned. We will not go easy on him."
A spokesperson from the police added: "It is very rare not to see the people in Greece wearing one because everyone is trying hard.
"He is not above the law and we will not hesitate to arrest and fine anyone who comes here."
On Thursday, Johnson was photographed popping into a newsagent in London without a face covering - despite the threat of a £200 fine for anyone refusing to wear one without a valid reason.
When approached about his lack of mask by The Mirror, he explained that he was not 'up to speed' with the most recent rules, before apologising and admitting that was 'no excuse'.
He said: "I was maybe not 100 percent up to speed but that was my first day back in England after three weeks not in England.
"So they [the rules] may have changed in that time. I'm not really a big shopping man.
"I'm extremely sorry for the slip up and I would urge absolutely everybody to do everything they can to make sure they do follow the rules about masks and social distancing.
"The fact this was my first day back in the UK after three weeks abroad is, I am sure, no excuse for not knowing the rules."
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