I'm in the camp that thinks that if he/she gets caught, he/she's only got himself/herself to blame.
As for the CAA investigating it; they should spend more time investigating flying schools that permit their students and instructors to hover taxi single engined helis at 20ft+ agl. Far more risky than flying under a 100ft high bridge and far more prevalent. OK so it's not illegal, but the potential for injury to self and third parties is significantly greater than flying under said bridge.
J