Jenny Reeves (@Jennyflyer1) was one of the first to post a picture on Twitter.
And Transport for London sounded the all-clear after the "invasion" had been averted.
The filming of Doctor Who has finished at Westminster Bridge, the Daleks are in the process of being removed.
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Services on major rail routes between London and south west England have been severely disrupted after a person was hit by a train.
The business executive, whose ruthless interviewing technique has won him many fans, is replacing Nick Hewer, who quit after a decade.
Recent opinion polls show Labour within striking distance of capturing the trophy seat of Finchley and Golders Green.