Hi Honesty!
By any chance, when you look at the underside of the crown, is there a plate with a threaded hole or two? If so, that's where Thorn attach the front mudguard. After removing the mounting bracket, they drill a hole through the 'guard and secure it in place using a 5mm bolt.
The threaded hole on the front of the Thorn fork crown is for mounting a head light.
Hope this helps.
Best,
Dan.