Free speech

Does anyone know the status of free speech in England? While I was wandering by the Exchange in London at about 22:30, I was stopped by a couple of bobbies, who wished to know the identity of the rolled-up poster that I was carrying. Because of massive protests scheduled for the G20 the next day, the police were out in force that night, and they were apparently confiscating protest materials. Fortunately, my poster was a map of the London Underground (a miracle of design, by the way). Me and the bobbies did some joking about how any representation of the Underground was inherently a protest, and we talked about my being from Ohio, and then they let me go on my way. I, being slightly flustered, didn’t get a picture.