They amount to penalty charges, which are unlawful.
What if they were £50. What if they were £100. What if they were £10,000.
People are forced to have bank accounts - Various laws (and combinations thereof) require employers to pay into bank accounts, and for benefits to be paid into bank accounts.
Sometimes, people fuck up, and go overdrawn. Penalising them for this is unlawful.
The combination of having to have an account, of having no choice in account, and being bent over a barrel and buggered, is what makes it unfair (as per UCTA at UCCTR).
Good point, well made.