How to logout a user who is logged in using HTTP Authentication

I did misunderstand - and now I realise that the problem was failing to clear the caches at the outset. As a result, people who had logged out still had access to the restricted template. Also I interpreted the guidance next to the HTTP Auth setting in the template access dialog as meaning that setting HTTP Auth was the only way to force users to login. Problem solved. Thank you for your patience and help, Ingo and Derek