Grrrrrr

That's a real pain. If it's down to the bare metal, squirt some aerosol etch primer into the can's cap, and then apply it to the metal with a fine paint brush. That'll stop it deteriorating further. Then you've got to decide whether to go to the professionals or touch it up yourself with a Jaguar Pacific Blue touch-up kit (paint + lacquer).

I've recently had to touch up a small patch on my X-Type. I found an effective technique was to apply the paint layer, wait 2 hours, flatten it in with your thumb; then apply the lacquer coat (which dissolves the paint and blends it in), wait another 4 hours, then flatten it with your thumb and Maguires scratch remover (which is little more than clay slip). Repeat the last step until you're satisfied with the finish, then leave it 24 hours before polishing with your favourite polish. The thing about paintwork is that you can always have another go for a better finish, if you fail at first attempt.