The police said an elderly man was pushed off a train on the Victoria line southbound between Green Park and Pimlico on Friday March 10 at around 1.30pm.
A man who was travelling on the service became abusive and loud, before pushing the man from the train at Victoria, the police said.
A 33-year-old man and a 22-year-old woman challenged the behaviour of the man.
A spokesman from the British Transport Police said: "Members of the public who tried to intervene were abused with homophobic and racist language."
The victims left the train at Pimlico, where the abuse continued until the man left the station on a northbound train.
Police have released an image of a man they would like to speak to in connection with an incident.
Officers believed the man may have information which could help with the investigation.
If you recognise the man in the image, British Transport Police urge you to contact them by calling 0800 40 50 40 or you can text information to 61016, quoting the reference number 194 11/03/17.
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