By coincidence, I just finished reading an article on medium.com by Nafeez Ahmed called " Death, Drugs and HSBC"
It's a lengthy read but ties in nicely with this thread. To sum up, HSBC have basically been illegally applying debt recovery charges to consumers. A whistleblower highlighted this, but , because of the structure of HSBC's ownership, the story has been prevented from being aired.
If HSBC were to be prosecuted up to 600,000 customers would be entitled to compensation averaging £1500 per customer.