A 16-year-old boy has been arrested in west London on suspicion of the commission, preparation or instigation of acts of terrorism, Scotland Yard said.
He was detained after officers searched a house at about 9.55am on Wednesday.
A Metropolitan Police statement said: “During the search, officers discovered cannabis plants as well as what is believed to be an imitation firearm. Further searches were carried out in the address and officers found items containing an unknown substance.
“As a precaution, specialist officers were called to the address and are now in the process of recovering the items, which will be sent for urgent analysis to determine what it is. Cordons remain in place around the address.”
The teen was initially arrested on suspicion of possession of an imitation firearm and cultivation of cannabis. He was further arrested on suspicion of commission, preparation or instigation of acts of terrorism under Section 41 of the Terrorism Act 2000.
He was still in police custody on Thursday, with the Met’s Counter Terrorism Command leading the investigation.