Perfect! That works nicely.
I was confused because the configuration of the virtual host ports is split across /etc/apache2/ports.conf and /etc/apache2/sites-available/default
Do you know why this is? Why not just have it all in the one file? (I've stuck the NameVirtualHost definition for port 443 into the ports file and not the 'default' file).
Also, and as an aside, why won't AllowOverride in .htaccess work with SSL? (I get a 500 error if I have AllowOverride on the webserver's ssl directory).