Network Rail told ITV News that there is no gas leak at London Bridge station and that train services are running as normal.
They added that four people were taken ill but the incidents were not related to each other.
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Some 66 people have been killed after the plane they were travelling on crashed in southern Iran.
The letter calls for an end to harassment, abuse, and impunity in a world "ripe for change".
Police say that anyone who sees Whitehouse should not approach him, but instead call them on 999 and quote incident 23 of 18 February.