It’s not every day that a foreign leader feels the need to publicly criticize an American pundit, but under the circumstances, British Prime Minister David Cameron was on firm ground yesterday.

British Prime Minister David Cameron had harsh words for the Fox News guest who on Sunday said the British city of Birmingham was “totally Muslim.” During an interview on Monday with ITV News, Cameron called Fox News “terrorism expert” Steven Emerson a “complete idiot” over the comments.

Specifically, the British prime minister said, “When I heard this, frankly, I choked on my porridge and I thought it must be April Fool’s Day,” adding, “[T]his guy is clearly a complete idiot.”

In a separate interview, Gisela Stuart, who represents Birmingham in the House of Commons, added , “I checked whether this was some kind of early April Fool spoof, and then I thought he was talking about Birmingham, Alabama. But then I realized he was just utterly and completely wrong.”

To appreciate why British officials were so irritated, it’s important to understand just how far Fox News’ Steven Emerson went during his on-air interview with anchor Jeanine Pirro. Emerson, presented as an “expert” on counter-terrorism, told a national television audience that the population of Birmingham, England, is now “ totally Muslim ,” and has become a city where “non-Muslims just simply don’t go.”

He added, “[P]arts of London, there are actually Muslim religious police that actually beat and actually wound seriously anyone who doesn’t dress according to religious Muslim attire.”

Pirro not only failed to push back, she actually endorsed the bizarre thesis. “You know what it sounds like to me, Steve? It sounds like a caliphate within a particular country,” the host replied.

You can probably guess where this is going.

In reality, Birmingham’s Muslim population is 22% , not 100%, and plenty of non-Muslims live in, and go to, the city every day. There’s also no such thing as “Muslim religious police” – in London, Birmingham, or any other part of the UK – beating anyone.

Emerson appears to have made the whole thing up.

The conservative pundit later apologized for what he described as an “inexcusable error” and said he would “make a donation to Birmingham Children’s Hospital.”

But for many Brits, Emerson’s contrition came a little late and the video of his ridiculous comments went viral. Over the weekend, #foxnewsfacts became a very popular hashtag, and an amusing way to poke fun at conservatives’ anti-Muslim paranoia.