I've now generated a new GPG-key for myself:
$ gpg --fingerprint 229A4066 pub 4096R/0C626242 2014-03-24 Key fingerprint = D516 C42B 1D0E 3F85 4CAB 9723 1909 D408 0C62 6242 uid Steve Kemp (Edinburgh, Scotland) <firstname.lastname@example.org> sub 4096R/229A4066 2014-03-24
The key can be found online via mit.edu : 0x1909D4080C626242
This has been signed with my old key:
pub 1024D/CD4C0D9D 2002-05-29 Key fingerprint = DB1F F3FB 1D08 FC01 ED22 2243 C0CF C6B3 CD4C 0D9D uid Steve Kemp <email@example.com> sub 2048g/AC995563 2002-05-29
If there is anybody who has signed my old key who wishes to sign my new one then please feel free to get in touch to arrange it.