There is usually a media ban on the reporting whenever a trial is conducted. If they happen to report anything like that during a trial they should be in contempt of court because any sort of interference could become a biased verdict. So essentially they didn't book him for freedom of speech rights, he was breaking the law.

Source: https://www.theguardian.com/uk-news/2018/may/29/edl-founder-tommy-robinson-jailed-13-months