A 24-year-old man from Sutton was arrested on February 26 at Stratford station on suspicion of outraging public decency.
It comes after a man is said to have sat opposite a woman on the Northern line between Balham and Old Street and begun to masturbate while staring at her.
The alleged incident happened at around 11.40pm on August 22, 2024.
The police issued an appeal for information on February 25.
A British Transport Police spokesperson said at the time: “Detectives are also appealing to anyone who may have experienced similar incidents, to report it.
“All reports of sexual assault are taken seriously and any information provided can help build a bigger picture.”
