In the lead-up to the startling vote there to leave the European Union, and for many years before, the larger and more conservative newspapers ran aggressive campaigns pushing for what became known as Brexit.

One of the biggest proponents of the exit was former Mayor Boris Johnson of London, who was, after all, a onetime reporter for The Times of London and The Daily Telegraph, where he still writes a column. (He was fired from The Times for fabricating a quote.)

As Martin Fletcher, a former associate editor of The Times of London, wrote last week in The New York Times, Mr. Johnson made his name as a journalist writing about the plans of bureaucrats in the European Union to “ban Britain’s favorite potato chips” and “standardize condom sizes.” The articles, Mr. Fletcher wrote, “bore scant relation to the truth,” but they helped spawn an anti-European Union movement in British journalism just the same.

As the vote approached, pro-Brexit newspapers — including The Sun, The Daily Mail, The Express and The Telegraph — wrote stories that exaggerated how many immigrants were coming to Britain because of its E.U. membership and their effects on social services, reported that Queen Elizabeth II was secretly pro-Brexit, and quoted claims from pro-Leave politicians that Britain was sending 350 million pounds ($464 million) a week to the European Union that could be used instead to shore up the National Health Service.

The Independent Press Standards Organization in Britain issued several rulings for inaccuracy — including one for the headline “Queen Backs Brexit,” which ran in The Sun. But the partisan press climate meant all facts were up for debate. Nothing could stand out as Platonic truth.

After the vote passed, Nigel Farage, a leading Brexit campaigner, said the Vote Leave campaign had been mistaken in saying the savings from the £350 million that supposedly went to the E.U. — itself misleading — could be used for the health service. That was followed by various expressions of regret by some pro-Brexit voters who now believe they were misled.

“The context for the referendum vote was a public which had been poorly” informed, “if not misinformed about the issue,” the former Guardian editor Alan Rusbridger told me.