Hammersmith and Fulham Council said officers were called just before 8 p.m. after a man was reported to be shouting abuse at people in the street.
He is alleged to have visited three supermarkets, including Tesco, Waitrose, and Sainsbury’s, in Fulham Palace Road, and injected foodstuffs using a number of syringes.
The man has been taken into police custody accused of trying to cause public harm or anxiety.
The supermarkets have been closed and crime scenes are in place.
The affected items are believed to be processed meat and microwaveable products, according to the council.
It is currently unknown how many items have been contaminated, or with what substance.
Hammersmith and Fulham Council issued an “emergency alert” notice on its social media accounts on Wednesday evening.
It said: “Members of the public are advised as a precaution to dispose of any food items bought from these supermarkets this evening.
“H&F Council’s Environmental Health team are now working with the supermarket branches affected.”
The Metropolitan Police has been approached for comment.
By Ted Hennessey