I have been told the only way to setup a Acatel 510 with a Linux server, with the linux server using the single static IP address is to use pptp. The idea is you do pptp from Linux server thru the router to the plusnet so only use one IP address.
The problem is it means the Linux server has to do the authentication with the service provider instead of the router. I do not know how to set-up authentication on the Linux box? I have been given an pptp profile for the 510 which has I am told worked ok on Windows.