Apologies for the delay in responding.
I have still failed to resolve this.
linux-azov:/ # chown -R steve /media/disk/
chown: changing ownership of `/media/disk/': Operation not permitted
I've entered the above as root.
Not sure whether the following helps (fstab):
/dev/sda1 /media/disk vfat users,gid=users,umask=0002,utf8=true 0 0