Wait, what? Battersea rehomed to you a 'seriously aggressive' dog?! Seems strange? What has been happening in the lead up to the bites? Battersea has behaviourists on call who would help I'm sure if you contacted them.
I've owned and trained JRTs and they can be feisty, stubborn little dogs with huge egos. They're also very smart, learn quickly (although not necessarily things you might want them to learn), brave and if not provided with enough entertainment will quickly make their own. They are independent by nature, having originally been bred to go to ground to bolt foxes from or hold them at bay in an earth until dug down to by hunters, who would be guided to them by sound; a quiet terrier was no use. So yes, they bark. It was part of their job. They also have lightning fast reactions (from dealing with vermin) and are well equipped with tooth and claw, also from their original job. They're not the most patient of dogs: they want it (or they want it to stop) and they want it (or want it stopped) NOW. Please keep up! Paying attention around possibly difficult times (taking something away they shouldn't have, grooming bits they don't like being touched, etc.) helps a lot.
The trouble with training a JRT is their hard-wired independence. They want to know 'what's in it for me' if they do what they're told, rather than having the in-built desire to co-operate that other types of dog are born with. Find the 'key', what makes them tick, and you'll have a fun, loyal, all-round good companion. Best dogs in the world. Don't find it, and you could find yourself being run rings round. Had you done any training with your boy, up to the three-hour behaviourist's visit?
I think you might find he will quickly see through the dropped keys or whatever. Is that all that happens? Big deal. What are you doing after you drop them? Is that the only consequence? Just telling him to stop barking? Is there any reward?
Bottom line is, aversive methods wear off and sometimes leave damaging side effects, particularly if they have been escalated. Positive methods last, and while appearing to be slower to get going, leave happier dogs and people once the penny drops.
There are literally millions of dogs eating before their owners, going through doorways first and getting on the sofa for a snooze without attempting world domination.