Any source?

I thought that it is years since you can have an UK "business" address and incorporate a company remotely (example):

https://www.rapidformations.co.uk/blog/can-a-non-uk-resident...

Needed papers may be much more than what is needed for Estonia, and most probably taxes/fees will be higher, so that Estonia may be a cheaper solution, but it is not like it is a "brand new concept" unavailable before.