The incident involving Katherine Blair is being linked with another attempted robbery nearby half-an-hour earlier. Met Police say: "On both occasions a firearm was seen but not used - no shots were fired. "None of the victims were injured and nothing was stolen during the incidents."
The first incident happened in Boston Place at 8pm involving a female victim and a male suspect.
More top news
More than a tenth of the Piccadilly Line train fleet is out of action because of emergency repairs to damaged wheels.
Rows of students stood and turned their backs before filing out of the lecture theatre.
Effie the endangered Western lowland gorilla has given birth to a healthy baby boy at London Zoo.