[Reverse light not working]

Reversing light stopped working (2008 Defender Puma 110).  After reading forum threads I checked fuse and replaced reversing light switch. Frustratingly, this did nothing. I swapped the fog light with the reversing light so I could manually have illumination. Weeks later I noticed both rear number plate bulbs had blown and replaced them.  As if by magic and perhaps by complete coincidence (as I can see no logical explanation), the reversing light (swapped back) is now working again and has continued to work since.