I was randomly stopped at Doncaster. "Do you mind if I search you, sir?" Well, naturally I did mind and said so. The security guard then said that he couldn't search me if I didn't give permission! I didn't press it, because I am 100% certain that if I had not let him search me I would have got no further, so it seems you have rights but you are in no position to assert them. The guard said that being searched was for my safety; my feeling is that searching ME has nothing to do with MY safety - my search would be assured by searching everyone else!
Incidentally, as you arrive at security at Doncaster you have to pose at a desk for a photo to be taken. The very nice lady explained to me that the strip on the boarding card is linked to the photo - "it's extra security." Which is something of a nonsense, because the officials at the gates were nowhere near the computer screens that could have shown these photos when they took the cards! I don't remember ever giving my consent to having my photo taken when I booked - even the police have to charge someone first!
(I travel frequently between UK and France - holiday home - and have now experienced similar nonsense at the docks. On my last crossing my car was diverted into a shed, the doors were closed and and official wanted to know if I had any guns, any weapons, any knives etc etc. I answered no and he took a cursory glanse in the boot. It was ony the following day when unpacking that I remembered the garden shears! Anyone ever heard of a ferry being hijacked by a terrorist waving a pair of garden shears?)