I from the US, just learned about these today, and had a chuckle.
an essex girl was driving down the A13 when her car phone rang. it was her boyfriend, urgently warning her “treacle, i just heard on the news that theres a car going the wrong way on the A13. please be careful!” “its not just one car!” said the essex girl “theres hundreds of them!”
Not from the UK - why is it Essex in particular?
It’s tricky to define but it has to do with proximity to London (Capital city) and the developing existence of influencers or (it girls) as they were known, combined with poor education and you had a generation of glamorous idiots, that were identified as being from Essex early. Think early Kim Kardashian such as Jordan https://en.wikipedia.org/wiki/Katie_Price
I would say Essex is stereotyped as being relatively affluent but lacking class, and is often a source of jokes.
I tried to find a succinct explanation but couldn’t so if you want a long read