If I said I was 'nebby' or 'having a neb' would you know what I meant?
Ourman, being the only commenting reader in Newcastle, has proved my theory that it's a dialectal word. 'Nebby' is nosy, and 'having a neb' means having a nose through something you shouldn't really. To me, it's slightly milder than nosy - nosy is a bit more insulting, to me, but that might be an incorrect interpretation.
Like I said before, there's still quite a lot of Geordie dialect out there.