A door-to-door saleswoman was attacked at knifepoint in an alley next to Finchley Road and Frognal rail station.

Police said: “A lone female was carrying out door-to-door sales and walked to an alley where the suspect attempted to sexually assault her at knife point.”

When police arrived the suspect had fled.

“During enquiries by police security at the Dury Centre, we believe this male may have tried this on another female,” said police.

Officer cordoned off the scene while CID and forensic units investigated.

Police said: “A dog found items which may be relevant but require examination.”

The victim was not physically injured in the incident which happened at around 8:30pm on Tuesday.