I am having similar problems although it us not just related to financial sites. It also is affecting itunes, halifax, next, mfi, thetrainline, and parts of BT! I am sure there are more out there but ...
i completely removed Norton and switched off the firewall protection on the livebox and can still not access these websites. And I have removed all of the latest windows updates.
Is believe Orange has a problem with their security settings as Orange is refusing access to a number of websites such as halifax.co.uk, phobos.apple.com (itunes music store), next.co.uk, mfi.co ...