Hi,
It uses the same key as the rear spare wheel compartment door budget locks, that I believe your mechanic was just able to get open?
The tool is the same “C.2798 Budget Lock Key” that Rob posted a photo in this other thread: How can we open the wheel compartment of Mark V?
Also known as “Tee Key” or T-key according to the shape, although the MKV tool is really an “L-key”.
The chrome escutcheon fitting is the same part as used on early E-type “Open Bonnet Latch” cars, and thus easily available, I believe I have 3-4 pcs extra! 
(BD.2551 Bonnet lock escutcheon)
Once you open that budget lock the spat will open and can be swinged down so that you can lift the front up and slide the rear pin out of it’s bracket and lift the whole spat off the car.
Or has someone fitted something else in there? I am not 100% sure of the photo.
Cheers!
Pekka T. - 647194 -
Fin.