For what it’s worth, one of the TSA agents in a PreCheck lane said that Rolexes are one kind of watch which is more likely to set off the metal detector. (And, I wasn’t wearing one; nor, do I own one.) So, based on the information from the TSA agent, I would be inclined to be less suspicious about the incidents you’ve relayed which occurred at Heathrow. It is entirely possible that the security folks were simply trying to prevent the watches from setting off the metal detector.