Graham,
This happened to me on Windows 7 with the US 2007 version. I believe that it happened when I changed my desktop theme from Aero to classic. I found it was necessary to manually add back the sounds. I not sure about the UK version, but in
my version you do that with Tools>Settings>Program Settings>Sounds. It's rather tedious to manually select a sound for each action, but that did bring the sounds back.
If anyone knows how to restore the default sounds, please post.
Bill Becker