It looks like you've figured it out now. The reason (in case it is of interest to others) is that you had set up www.force.org.uk to be a frameset containing your site on voice, rather than configuring the DNS of www.force.org.uk to point directly to the e-voice server.
In the former situation, the URL doesn't change when you navigate because the navigation only affects what's displayed inside the frame, not what's inside the main browser window.
In the latter case, providing you have configured your site to use your chosen domain in the site settings, then you simply point your domain to the voice server using DNS and Voice does the rest.
This also means that Voice will use your domain in the A-Z index, and redirect anyone visiting your site on the e-voice.org.uk domain to your personal domain name.
Joe - Voice Admin