if it is safe for you to prooceed then you can do so, if there is another car blockig your way or the ligths are red, you now know that it is illegal to cross the white line so you will have to wait there until they change

it's not you being an arsehole baout it, but the copper gesticulating at you isn't going to pay your fine or take your points if you should get caught on camera or reported

and if you are taken to court and reported for being a hindrance to a police officer in the enactment of his duties you can cite this as the case and no court in the land will prosecute you for this

can you imaguine the uproar it would cause if one law states you must allow the policeman through and yet, at the same time, you have to break another law to allow him to do so?

the justice system would be turned on it's head and you'd be walking away a millionaire when you took it to the highest courts in the land and europe