How to explicitly revoke access to pages

Hi guys,

I have tried numerous plugins but none of them achieve what I need.
Basically I need to revoke access to pages for particular users/roles.

By this I mean.. I can already display menus based on the login, however, this does not stop the user accessing a page if they know the URL.

Is there anyway I can stop this from happening and give them an error if they try to access a url directly which they are not allowed to see?

Thanks
Immy