Image copyright Reuters/BBC Image caption Boris said he thought the term was from Roald Dahl's Charlie and the Chocolate Factory

Did Boris Johnson just use a word from Charlie and the Chocolate Factory to insult Jeremy Corbyn? Well, he thinks he did.

In his first interaction with the election campaign, the foreign secretary called the Labour leader a "mutton-headed, old mugwump", leaving voters (and journalists) a little bemused.

BoJo - as the tabloids like to call him - launched his attack on Jeremy Corbyn in the Sun. His words have been derided as "look at me name-calling" by Labour.

It's not the first time politics has seen someone called a mugwump. Boris himself was branded one by Conservative MP Nicholas Soames last year.

Image copyright Twitter

So what does mugwump mean?

Boris has said he thinks it's from Roald Dahl's 1964 book Charlie and the Chocolate Factory.

Speaking on ITV's Good Morning Britain, he said: "I think Willy Wonka says it either to the parents of Violet Beauregarde or Augustus Gloop."

In fact, the word appears not in that book but in the follow-up, Charlie And The Great Glass Elevator.

In the 1972 tale, chocolate factory owner Wonka refers to a character as "my dear old muddle-headed mugwump".

Dahl's story The Twits - published in 1980 - references a similar word when it features a character named Muggle-wump the monkey.

The Oxford English Dictionary defines mugwump as someone who remains aloof or independent, especially politically.

It also says mugwump was used to refer to people who left the Republican Party in 1884 to support the Democratic candidate Grover Cleveland.

For some time afterwards, the word was used in the US to describe a political turncoat.

Boss or wizard?

However, the term appears to have been in more positive use in the mid-19th Century, when it was typically used among native Americans to refer to an important person, a leader or a boss.

That meaning probably wasn't the one Boris was drawing on.

Similarly, others will know that the Harry Potter books have referred to mugwumps to describe members of the International Confederation of Wizards, of which Hogwarts supremo Albus Dumbledore was appointed as the Supreme Mugwump.

The word also featured in the graphic and surrealistic novel Naked Lunch, by William S Burroughs, as the name for a reptilian alien species.

And in 1994, Britain's music charts got a taste of the mugwumps when Bomb The Bass mentioned them in the chorus of Bug Powder Dust, paying tribute to Burroughs' book.