I still go back to: If this was so secret it's still classified to this day, why is it flying around Scotland near the town of Calvine? If it's US Navy super-secret radar research, why do it at Mull of Kintyre? They have the Fallon Naval Air Station smack in the middle of Nevada.
There are a number of possible, even likely, answers to your questions:
If the object shown in the Calvine photo is a classified/stealthy ISR platform, why was it flying around Calvine/Scotland?
The photo was taken two days after Iraq invaded Kuwait, a military action that threatened to both impact oil production/shipments from the ME, and spread military conflict across the region. Specifically the US/UK were concerned Iraq might continue on into Saudi Arabia, and such concerns would have justified the use of the most capable/survivable ISR platform available, even if that platform was still in EMD. Knowing whether the West had to act immediately or had time to build up forces was critical relative to logistical decisions.
It would make sense to stage that ISR platform closer to the ME during conflict to a facility/base where we had a high degree of confidence in both security and support capabilities. The obvious choice would have been somewhere in the UK where we have bases/personnel and operate under the "special relationship" with the Brits.
The Harriers are also reasonably explained. Ever classified a/c suffer from inflight emergencies (IFE), anything from lightning and bird strikes to system failures and human errors. It's not uncommon for an a/c that has declared (or had declared) an IFE to have another a/c join the mishap a/c for a visual inspection of any damage, take video if possible, and (hopefully) escort the mishap a/c to a emergency landing if necessary.
I can say with a high degree of confidence, if the object in the photo is/was a classified ISR platform, if was not a manned USAF aircraft. US Navy? Non DoD/OGA drone? Maybe, I don't know. What I do know is it's entirely possible it could still be classified, because there are USAF a/c from that period that have not been made public.
One other possibility is the Brits were developing an advanced air defense radar system called UKADGE--United Kingdom Air Defense Ground Environment at this time. Could the object have been brought to the UK to be tested against this new radar system? Sure, foreign comparative and dissimilar testing of military equipment among friendly nations is very common.