Exiv2

I'm living in London. I had my Nikon D70 clock set to the correct BST
during summertime (i.e. GMT +1 hour).

I have now uploaded some pictures and am renaming / processing using
exiv2 utility.

exiv2 shows the Date and Time stored in the NEF files correctly (e.g.
a photo taken at 12:04 on 2nd Sept shows "2006:09:02 12:04:49"

Now this is stored as an ascii string (I understand) and there is no
TimeZone info in the camera or the NEF file.

So when I ask exiv2 to re-touch the file to the exif timestamp
(exiv2 -T mv DSC_3142.NEF)

it actually sets the file creation time to 2006:09:02 13:04:49

This is obviously an hour out.