A man has been arrested on suspicion of inciting racial hatred after allegedly posting a tweet in response to the Brussels attacks.
The tweet read: "I confronted a Muslim woman yesterday in Croydon. I asked her to explain Brussels. She said 'Nothing to do with me'. A mealy mouthed reply."
Matthew Doyle, 46, was arrested on Wednesday night in Croydon.
He has since been taken to a south London hospital after he "expressed concerns for his health", the Met said.
Police would not confirm whether the arrest relates to the tweet which went viral or to other statements on social media posted by the same user.
At least 31 people were killed and scores injured when bombs went off in the Belgian capital on Tuesday.
The post was widely mocked on social media and spawned a wave of parodies.
One man wrote: "I confronted an Irish women yesterday in Camden. I asked her to explain Bono. She said 'Nothing to do with me'. A mealy mouthed reply."
Lisa Holdsworth wrote: "I confronted a woman in Croydon and asked her to explain shredless marmalade. 'Nothing to do with me'. A peely-mouthed reply.
Scotland Yard said Mr Doyle had been taken to hospital "as a precaution".