A "v" indicates a virtual package.
An installed package would have an "i" to the left of the entry.
Anyway I've just solved the problem. I did aptitude search on "locales" and got a "B" to the left of the "locales" entry in the resulting list of packages. I think this means broken, so I did "aptitude install locales". The result was that glibc was installed as a dependency. I have now done "aptitude safe-upgrade" and all went well.
However, I have no idea why I appear to have lost glibc in the first place.
Thanks for your assistance,