I've now tried removing both SQL Server 2008 R2 and Visual Studioo 2008 using Add/Remove Programs (as far as I can tell), including setup files, visual studio shell, etc.
I then install Visual Studio 2008, added SP1 and applied current updates. SQL Server 2008 R2 still complains about previous releases of Microsoft Visual Studio 2008!
Clearly there's some registry setting or file that's not been reset properly. Can someone point me in the right direction?
(P.S. Is it worth starting a new thread since this one's been marked as answered and I'm sure someone from the SQL Server development group would be able to say in a couple of minutes what's actually being checked for and hence how to fix this? If I
don't get an answer soon I'm going to have to log it as a support call.)