Access to password protected subsite

‘Members1’ is a private members subsite of ‘Hampstead Bowmen.com’ there is a login page requiring user name and password. Every thing works fine except that – if someone happens to know the URL/path and enters it in browser, they are taken into the private ‘Members Area’ and they can view the content and the bbpress forum located there, but they are not logged in and cannot post etc. Can I prevent this and redirect them to the login page?

Also, when club members receive an email notification of a new topic or post in bbpress and follow the link provided, the result is the same as above! But (of course), in this case, we do want them to be logged in and be able to reply to a topic etc. I’m thinking this is a related issue?
Any help would be much appreciated,
Russell