Boris Johnson wed Carrie Symonds in a small ceremony at the Catholic Westminster Cathedral on Saturday, despite being twice divorced.
But as neither his six-year first marriage to Allegra Mostyn-Owen, nor his second 27-year marriage to Marina Wheeler were Catholic ceremonies, in the eyes of the church they may be invalid.
Matt Chinery, an ecclesiastical and canon lawyer, told Times Radio on Sunday: “There is a requirement if you are a Roman Catholic that you must have your wedding overseen by a Roman Catholic priest or deacon.”
He explained that any other form of marriage “is not valid unless you had previous permission from your bishop to marry outside of the Catholic church”.
Boris Johnson was baptised as a Catholic, but was confirmed as an Anglican as a teenager.
Mr Chinery explained: “What I think has happened here is that the Catholic church has looked at Boris Johnson’s first two marriages (and) seen that he’s a Roman Catholic by baptism.
“They’ve looked at that, said ‘you are a Catholic because you were baptised Catholic, your first two weddings weren’t in a Catholic church overseen by a Catholic minister therefore the Roman Catholic church does not recognise those two marriages as valid’.”
He added: “So in the eyes of the Catholic church Boris Johnson woke up last week as somebody who wasn’t married and had never been married and so was free to marry in the cathedral this weekend.”
Catholic writer Catherine Pepinster was of the same view.
She told the Mail on Sunday that as Mr Johnson’s previous marriages were “in non-Catholic settings”, the church did not recognise them.
“As far as the church is concerned, this is his first marriage,” she said, adding: “The others don’t need to be annulled.”