The Metropolitan Police had said they pulled a woman from the water after MP Stephen Gilbert claimed he rescued her:
"At 1950 the marine policing unit responded to reports of a woman in the River Thames near Westminster Bridge. They recovered her from the water and took her to hospital. Next of kin have been informed," the force said in a statement.
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The ship sent out a mayday call amid strong gusts, local authorities say.
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It has had the highest rate of sign-ups on record, according to Parliament’s official Petitions Committee.