It all worked OK for me. Overall result is an up to date map now and then further updates for the next 12 months, all for £6.95 in my case
I had to download ‘TomTom Home’ first though (when prompted to do so): http://www.tomtom.com/services/service.php?id=16&tab=87. My spare sat nav is quite old and I have since upgraded my computer so I needed to compete this step first.
If you get an error message it might be worth clearing the history on Internet Explorer and then trying again (e.g. ‘Tools’, ‘Internet Options’, then under ‘Browsing History’ select ‘Delete’ - to remove temporary files, cookies, history).