I don't think this is correct. You are covered £50K per authorised institution . If you lose £1million by having £50K spread across 20 different institutions you will get £50K for each one. Most people think that if they have their money in 2 different banks they are covered for £100K, but this isn't the case if both banks are owned by the same institution.
My broker is in the USA and by law they must keep client money in a segregated account. This protects clients against broker bankruptcy, but(!), if the financial institution that holds the funds goes bankrupt, you are not protected by The Federal Deposit Insurance Corporation (FDIC). You lose everything.
You’re right, I stand corrected!
http://www.fscs.org.uk/what-we-cover/eligibility-rules/compensation-limits/