I believe the police can, and routinely do, arrest people to further their investigations. Being arrested doesn't automatically mean a charge. So you have a sort of exchange that may go "We would like to interview you at the police station regarding this event". "I don't want to go to the police station"... "Then you are under arrest.... the purpose of your arrest is to enable us to continue our investigation" etc. Sadly, although an arrest doesn't imply any guilt etc, society thrives on "no smoke without fire".
Also, the way the law stands in the UK, anonymity/confidentiality is not a right although this is usually applied in very sensitive cases such as those involving children etc. where identifying a suspect may indirectly lead to identifying the victim.
The alternative to naming persons who have been arrested could lead something like the situation that used to exist in countries like Argentina and Chile with the "disappeareds".