I hesitate to challenge you on this, as you clearly know and work in the industry. 99.9% of the time I'd agree with your statement but, rather than derail the thread with excessive detail for others, I'll just say that Beaufort Securities put a very big challenge to this last year.
I did review some of that information/situation after a client challenged me on it.
My "understand", which may/may not be completely correct was that the Beaufort Securities had a UK arm and a US arm, this immediately complicates things. They went into administration and PWC (Administrators) tried to say the cost of the administration would be $100 over next 4 years!!! (nice money if you can earn it) - they eventually revised this down to something like £50 million over 2 years.
Beaufort Securities was more of a stockbroker who did a lot of penny stocks etc - super high risk stuff - So there was 2 parts to this -
1 - mis-selling of stocks - which would be a separate claim under FSCS
2 - administration/insolvency and loss of funds - some client money was not properly segregated from the main company accounts and therefore was "usable" by the administrators
However FSCS covered something like 94% of the costs for returning assets to approximately 17,500 retail and corporate clients.
They as a company were placed under supervision multiples times from 2016 by the FCA, and were still authorised (crazy) , but eventually they were insolvent.
Basically a very niche company, who were up to no good from the off.
Stick to regulated, large platforms/SIPP providers, ISA providers and large funds/investments and you'll be fine.
But fair point
@The_Abyss - you can never be too careful.
I remember having to claim myself for my cash ISA with Icesave...remember them....when they went bust. Got money back very quickly, to be fair.