Are you talking about Speaker's Corner at Hyde Park?
I can't imagine your brother getting arrested for reading the Constitution.
It might be a relief compared to some of the things said there!
I've been there a couple times, and there were people speaking freely about fairly outlandish topics. I know that religion is a popular topic there, but it was not the only one.
I did see a guy get arrested there once, and it turned out the reason was he was distributing some sort of flyer, which was illegal.
This man was arrested for saying homosexuality is a sin.
On one of the days I was there, a guy was speaking on the same topic (homosexuality), but nothing happened to him.