More detail: https://medium.com/wikimedia-policy/wikipedias-nonprofit-hos...
It seems to be a fairly standard judicial review: if OFCOM(?) class them as "category 1", they are under a very serious burden, so they want the categorization decision reviewed in court.
I think it will be very hard to write a definition that excludes wikipedia and includes (and I am quoting the article) "many of the services UK society is actually concerned about, like misogynistic hate websites".
Very interested how this goes.