The emails probably are forwarded but not accepted by the recipient mail service because many auto forwarded mail messages fail authentication. TalkTalk consumer mail messages use a strict SPF policy not to allow other than designated senders (that does not include talktalk.net) to send mail messages. The TalkTalk DMARC policy for the recipient is to reject unauthenticated mail.
Banks and Utilities also normally use strict authentication to avoid spoofing of their mail messages.
So, it depends on the receiving mail service and how that deals with unauthenticated mail. Gmail have ramped up their rejections of unauthenticated mail.
Look at one of the bank emails. View the source or header. Top line is likely to be Return-Path: What's the email domain quoted on that line. I'll look that up and give a view on what should happen to that mail message when auto forwarded.
