There were a few suggestions made but ultimately the only option that worked for my situation was a brilliant little application called IE PassView. It is available from Nirsoft here http://www.nirsoft.net/utils/internet_explorer_password.html. I see they have similar applications for router passwords, email passwords and Internet Explorer history but I haven't tried them.
I ran it from a USB stick and it showed me all the stored usernames and passwords and allowed me to delete them. Quite scary really! It also allows you to export them for backup etc
I post this in here in the hope that it will save someone else the hassle of searching. It does access and edit the registry so it comes with risks and anti virus/spyware programs alert on it but it seems to have a good reputation around the internet.