Linked to a mortgage mess up, tho not as bad as yours, my bank (different from yours) has also offered me �150 as compensation and paid back interest wrongly charged on my mortgage.
I am about to write back asking for a little more. A badly handled application, which took nearly 3 months to complete, cost me time, an unnecessary car journey of 250 miles, credit card interest, and if I hadn't already bought the place with cash, I would most likely have lost that to another buyer. I couldn't access my own mortgage funds locked at my solicitors causing a furious showdown in the bank foyer over their sheer ineptitude and lies.
I also want my branch to apologise for losing a hand delivered letter of complaint, to the manager, lost within her own branch.
No harm in asking for some more. Looks as if �150 is the industry standard starting point. But I dont expect they yield much.