OK, now I just saw this on the defra site:
Make sure the vet completes sections I to V of the certificate correctly and all the details in the following box. If the vet is not a government-authorised veterinarian, the certificate must also be dated and stamped by a vet authorised by the competent authority.
So if my vet is USDA accredited, does it need to be sent to the USDA office?
Yes.
It still needs to ultimately be sent for approval by the USDA office because they are the ones who look it over, see that YOUR vet is indeed okayed by them, see that all your pets paperwork and dates are in order, then signs off on the whole deal.
So in effect you have to have the TWO "usda vets" on the case, the one who deals with it hands on, and the major guy who signs off on it.
It goes like this:
Your own, personal vet who is hands-on dealing with your pet and your forms, yes, he or she must be USDA accredited. Some vets are on their list, some are not.
Now, even though your vet is "USDA accredited" he or she is not the one who actually does the final, grand, be-all-and-end-all signing off of your Form EU998.
He must fill it all out, but the final step is always that it must then be sent to the actual USDA headquarters. There, they have in attendance another "USDA vet" but this one isn't messing around with people's dogs and cats -- this one sits in the office literally looking at and then signing and stamping these things then mailing them back to you, the pet owner.
It is this "grand poobah" USDA vet at the headquarters of your region whose signature and embossed stamp on your form is the Holy Grail of your pet being allowed entry into the UK.
It's HE who has to look over the form your vet filled out, and approve of the fact that your vet is on his list of vets accredited at his office. That's why your own vet also has to be accredited in the first place. But the head guy is the ultimate authority -- this is the long way of saying, yes it ALWAYS has to ultimately be sent to the actual USDA vet in his office to be signed off on.