PPTP passthrough

Hi I was wondering about how to block or limit access through the PPTP port.  I have users using the PPTP port to passthrough to the server for authentication, so therefore have an untrust to trust policy setup.

I am getting failed logins on the server and suspect is through the PPTP port like I've seen elsewhere and have created a couple of policies to block all countries other than the UK for access and it doesn't seem to block anything.  I am unable to find the IPs these failures are created from like i have done before for other clients.

Basically i am asking how to properly setup a policy that will block all countries other than UK as i suspect the failures are coming from foreign countries based on the intrusion logs. 

I have address setup based on geographical location and a group with the countries in it and a policy created to deny anything from that group to the server on port 1723.