I would like to redirect them to the login page - on the CB configuration menu, registration tab, i have entered the following against the first login redirect field: /index.php/login but this doesn't seem to work.
I am not an expert, but if you go to Joomla Modules and search for Login, you should find the community builder login module (which you should be using).
Edit this modules settings.
Login options tab
You will see Login Redirection URL field.
You should type the URL you would like the user to go to and Save.