The WTS is "charitable" the way Bill and Ted were "guitarists".
As they are a 'church' - it would seem to be a legal requirement? They MUST be registered as a charity?
https://fiec.org.uk/what-we-do/strand-blog/do-you-need-to-register-with-the-charity-commission
"In England and Wales, a charity is any institution that is established wholly for charitable purposes. Most independent churches fall within this definition. Therefore, they need to register with the Charity Commission unless they are excepted from registration."
Many churches incorrectly believe that, because they are a church or a place of worship, they do not need to be registered. This is not the case. There is no blanket exemption from registration. Some, but not many, churches in England and Wales do not currently have to register. But these exceptions are now very limited and are subject to expected future changes in the law and to the changing individual circumstances of the church.