Sadly that kind of thing happens quite often, it’s not unique to Tommy Robinson. There were a lot of senior Conservative politicians at that march and they clearly didn’t want him there too.
So Tommy Robinson has apparently now been banned from entering London. But meanwhile, if you fly a foreign flag, you are free to deface war memorials and climb all over them, and have a bath in the fountains in Trafalgar Square, all the time calling for the eradication of the Jewish nation and its people. I'm not condoning what Robinson stands for at all, but it's more than a bit lopsided
Tommy Robinson is controversial figure. He still has right to assembly, to protest and report. This man was peacefully having a breakfast, he was being approached by people who were shaking his hand, having pictures taken with him, females kissed him, there was no harassment, or distress being caused. When Tommy Robinson left the cafe (?), the police in a very large group surrounded him, handcuffed him, and at one point pulled his head back and pepper sprayed him in the eyes, then dragged him to a police van. No, I do not think this thing happens frequently.
I agree that Robinson has the right to assembly, protest and report and unless he committed a crime, he shouldn't have been detained. Unfortunately, this kind of thing does happen frequently - you just don't hear about it because, as you say, Robinson is a controversial figure whose activities are reported on. For example, Graham Smith and several other members of Republic were arrested and held before the King's coronation for having a "means to lock on" (they hadn't). Members of Extinction Rebellion, Just Stop Oil etc have been detained on suspicion that they might commit a crime, or for being in an area. These occasions aren't reported on unlike Robinson's activities. All unlawful detentions are wrong in my opinion.
You have highlighted how different those cases where. The police broke an act here - Anti-social Behaviour, Crime and Policing Act 2014 (legislation.gov.uk) Tommy Robinson was being paid to attend as a journalist. In section 36 of the act there are restrictions ... I cannot think of many cases where police descend on a journalist, drag him through the streets and pepper spray him after being cuffed ... I feel the Met should have given Tommy Robinson the freedom they extend to controversial outspoken pro-Palestinian protestors. The police's uneven and violent treatment of Robinson is in a stark contrast to the can't see nuffin approach to anti semitic extremists who have been causing harassment, alarm and distress in London. It is a double standard in my opinion.