[gouranga]

For reference, having been on the end of it (at Waterloo Station [1]), the police also use another tactic regularly which sucks but is easily dealt with:

"I'll pepper spray you if you don't make a statement and say you were resisting arrest".

Make a fucking scene: "shout as loud as possible what the officer said". When there are a hundred eyes on you, they back off.

[1] I was going camping and had a hatchet inside my bag (not easily accessible) and was stopped and searched. It is definitely legal to carry such things as long as there is a purpose for it.