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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Donald Trump is to visit the UK on July 13 and hold bilateral talks with Theresa May, Britain's ambassador to the US has said.
The Football Association has announced it has received an offer to buy Wembley Stadium.
The most hotly-tipped date is July 13, following the Nato summit which the president is due to attend in Brussels on the previous days.