Many people and organisations share devices. If one person has logged into their account the next person to use that device is unable to make a booking as there is no log out button.
When a user arrives at the 'Login' stage of checkout, the user should be able to see what account is currently logged in. for example: "You are currently logged in as: X". This would help stop somebody from purchasing courses on someone else's account.
When someone has recognised that they are logged in as someone else, they should be able to log out. This should return the user to the shopping basket (with their items still selected). Then when they click next, the 'Login' page should display the log in form. If the user was to select log out and then the log in form was displayed, they would be uncertain of their baskets' contents.
These changes should be applied to the shopping basket itself and not hidden away in the header or footer as this is a prominent usability issue.
Many eCommerce sites already implement this feature, such as Amazon, ebay and ASOS.