That's a huge weakness when it comes to IB. With other brokers your money is in US and therefore under SIPC protection - $250k is significant for most retail for peace of mind.
Guys, please ... a little thought before you write !!!
You misunderstand the whole point about FSCS (or I assume SIPC too).
FSCS is predominantly there to cover cash, i.e. you have 85K in the bank, bank goes phut, your cash is protected.
With a broker, anything you trade on the stockmarkets (using cash, not derivatives like CFDs, spreadbets etc.) is either (a) held in your name on the records of the company you are trading (either directly on the company's share register or via a centralised system such as CREST in the UK) or (b) is held in segregated fashion in your broker's nominee account.
In the case of nominee accounts, these are seperate legal entities, specifically setup for the purposes of maintaining client holdings. They are completely ringfenced from any of the brokers other business activities, this is a legal requirement.
Therefore there will always be a firm audit trail that shows "those shares are Bob's".
Most responsible brokers will also hold cash in a segregated client account too.
So really, if you think about it, the likes of the FSCS is there as a last resort.
A well run financial operation should be able to wind-down its activities in a structured and responsible manner without its clients having to resort to government safeguards.
A badly run financial operation would leave you open to the possibility of fraud, negligence and gross administrative errors. Those are broadly the main three areas in which you would end up having to rely on government safeguards.
It is up to you to reach your own personal determination as to whether you feel IB is "well run" or "badly run", and therefore how likely you feel it would be you would need to fallback to last-resort government safeguards.