If it was up to the security types the requirements would change on a random requirements/rotation some days strict as hell other days next to nothing.
The whole point is they don't want any rules or procedures to be predictable or known.
The UK is a bit special anyway because it instigates tighter requirements than required. Airports have to show compliance with the minimum standard, there is nothing stopping them going further than the minimum requirement.
Manchester is a pain in the bum, huge security empire and it seems to be pretty much untouchable. There is huge gapping holes in what they do and a lot of things rely on people following the rules (how many people up to no good follow the rules?)
BTW the EU base rule is anything with a larger screen than 6" needs to be separate. But there is nothing wrong or illegal for an airport to insist that all devices need to be separated or for that matter everyone is required to take their shoes and belts off.
The grunts on ground are videoed and if they don't enforce the local rules they get the sack. So I do actually have some sympathy with them. There are of course nasty individuals with huge chips on their shoulders which cause major grief enforcing said rules. And there are nice people doing a job and make the process as painless as possible and a full range in between which may float between the extremes. Just like the people they are dealing with.
the only thing you can do is avoid the place if you can. I do know pilots that have changed jobs just to get away from MAN. Dealing with an engine failure was less stress than getting from the car to the aircraft.