So I phoned the FSA. The nice man there did some research and confirmed that there is no FSA requirement for banks to validate the full list of trustees: it’s a purely commercial decision. I reported this to the bank who is still trying to sort itself out. I’ll let you know the outcome.
But it’s like ’elth ’n’ safety: blamed for everything and causes common sense to go out of the window. Surely an established Church of England parish that has been around in some form for hundreds of years and can provide at least 20 names of its trustees can be trusted!