Officers arrested a man at the scene on suspicion of assaulting an LAS staff member.
He was taken to a west London hospital, where he remains in police custody.
The incident is believed to be mental health related.
A Met spokesman said: "Police were called to the incident at 10.53am.
"A man was arrested at the scene on suspicion of assaulting a London Ambulance crew member.
"He was then taken to a west London hospital for a health inspection."
LAS Assistant Director of Operations, Natasha Wills,said:
"We were called at 10.29am to reports of a person unwell at an address on Dickens Lane, Hayes.
"We sent an ambulance crew, a single responder in a car and an incident response officer to the scene.
"The crew member was treated at scene and taken to hospital. The patient was arrested by police and taken separately to hospital for treatment.
“We are doing everything we can to support the crew member. It is absolutely unacceptable that our staff are attacked or verbally abused whilst trying to do their job and care for patients."
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