Westminster Bridge was shut on Tuesday after police found an abandoned vehicle near Parliament.
Police shut off the busy London bridge after a SmartCar was left unattended near the House of Commons on Tuesday afternoon.
Photos show a bomb disposal robot being dispatched to investigated the car that was sitting in the bus lane.
Police said that they did not find anything suspicious and the owner of the car was later photographed collecting his vehicle.
It is not clear why it was abandoned on the bridge.
MPs said that they were evacuated from the library while the bomb disposal unit approached the vehicle.
Reports that police were investigating a "suspicious vehicle" led some to suggest that Vote Leave's official campaign bus might be the one causing the closure.
Ukip's leave campaign bus was also suggested as a potential suspect for the holdup.
Transport for London warned commuters that there could be delays caused by the closure.
Police announced that the road was reopened at 4.30pm.