A woman was sexually assaulted in Ilford on Thursday.
She was targeted in Clements Road by a man who groped her breasts.
The woman shouted to members of the public and one called the police before following the suspect to Ilford station.
The resident notified a team of street duty officers, probationary constables, who were manning a knife arch at the site for Operation Bigwing and the suspect was detained.
The man has been bailed to return to Ilford police station in August.
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