hi Andrew, McAfee and most other antivirus packages have to be re-newed each year.
When you re-subscribe you can continue to download updates for another year if you dont re-new you'll still have protection but it will not update to learn of new threats.
For McAfee you usually get an email that takes you to a renewal web site, just make sure you change it to UK instead of USA on the sign in screen as people forget and wonder why its in dollars.
Since McAfee 2005 peolpe have had to update to McAfee internet security suite 2006 for about £30 instead of renewing, so you'll likely have to do that online too.