Incorrect, loitering is not a crime in England or Wales. The Vagrancy Acts of 1825 and 1898 which made loitering a crime were repealed by a different law on Sexual Assault in 2003.
This gentleman had a right to be in a public place for his own purposes. He is not accused of committing a crime and the fact that other people may not like his presence is not his problem. The policeman was wrong and had no authority to arrest him.
https://en.m.wikipedia.org/wiki/Loitering
This article begs to differ. If you present a threat to the public peace, you can be arrested. The mandate in British founded countries is peace and good order. If you might violate that, you can be arrested.
https://www.theguardian.com/society/2018/may/20/homeless-people-fined-imprisoned-pspo-england-wales