You have one too many negative prefixes there. The Church of England is already established. Those who want to remove that status are proposing disestablishment. Antidisestablishmentarianism is the desire to maintain the status quo.

As someone else pointed out, you're over-negating establishmentarianism.

But it doesn't matter anyway - the UK is a pretty atheist society and getting more so... Those who self-describe as "atheist" in the census:

2001: 15.9%

2011: 25.7%

2021: 37.8%

In Scotland, figures are higher with a majority of the population now describing themselves as atheist (51.1%)

And these figures are only for people who describe themselves as atheists, not just agnostic. The number of people saying they believe "in god" was only 16%, and expanding that to "any god" bumped it to 27%, according to a YouGov poll in 2020.

Also, the most irreligious government ever is the most-recent one, with 40% of MPs opting to make a secular affirmation of service rather than swear a religious oath.

Basically the god-squad is done in the UK, it's just a matter of time - which is odd for a place with an official state religion, as opposed to somewhere like the USA which is officially non-affiliated with any religion, but has "christians" who wouldn't recognise Jesus unless he was white, toting an uzi, and telling them to give him money now to get a great afterlife - "prosperity gospel" my arse.

(Figures from: https://en.wikipedia.org/wiki/Irreligion_in_the_United_Kingd...)