A man who apparently attempted to sexually assault a woman in Dalston overnight was detained by a good Samaritan until police arrived.
Police are "urgently appealing" to find the woman, who ran away from the scene in Shacklewell Road after the witness intervened.
The Met says a 63-year-old man was arrested on suspicion of attempted rape and remains in custody.
Police were called at 12.18am on Thursday - March 10 - when it was reported that a man was trying to push a woman into a car and sexually assault her.
Det Con Joanne Gaffney of the Met’s Central East command unit said: "This woman has probably gone through a very traumatic experience and I fully understand why she ran from the scene.
"I want to assure her, or anyone who knows her, that we can offer her advice and support from specially trained officers who are sexual offence experts.
"I really hope she will contact police and tell us what happened.
"At the very least this would give us the chance to make sure she is okay and is supported - our first concern is for her welfare."
Officers don’t believe the woman was injured in the incident, Scotland Yard said.
Det Con Gaffney added: "Even if (the victim) does not want to speak to police, I urge her to speak with her doctor or those charities or organisations that offer advice and support for vulnerable women and not to shoulder this burden alone.
"I cannot stress enough that the well-being of this woman is our prime motivation.
"If you are the woman, or you know her, please do get in touch."
Anyone who has, or knows someone who has, been through a similar experience is also encouraged to contact police.
"Our specially trained officers are committed to doing everything they can to keep women and girls safe by placing offenders before the courts," Det Con Gaffney said.
"The first step in that process is victims coming forward."
If you saw the alleged incident in Shacklewell Road or have any information, please call 101 or tweet @MetCC, quoting the reference CAD116/10MAR.
Contact the independent charity Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org to give information anonymously.
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