I have created a page on episerver, and have given read access to just one account. This works as expected, in that when visiting the page, a login-prompt is seen, and when the credentials are entered, this account can view the page.
The problem is - once the user has authenticated once, there is no 'logout' option. This could result in the authenticated user viewing content, navigating away, but, then leaving the door open for an unauthorised user to view it - EG, if it had been accessed on a shared / public computer.
Does anyone have any ideas how to overcome this or how to force a log-out?
I assume based on your description that you are relying on the default EPiServer login (which is used to log in to online center / edit mode / whatever). So you have no login option on the site's templates?
The "default" logout option sits in online center, so users without access to that have to be given a logout option in the templates of the site. So if you don't already have it you'll have to implement it in your templates and place it somewhere the users can find it. You could for example display a logout link in the header of the site for logged-in users (and display nothing for anonymous users, unless you want to build a custom login as well). If you're lucky you can accomplish what you want just using the asp LoginStatus control.
You could add in the master page, forced logged out in PreRender, then you would need to login for each page request