CBRN experts from the Enfield Metropolitan Police Service went to Enfield Town Civic Centre on Friday after a council worker opened an envelope containing suspicious white powder.
The substance was discovered to be talcum powder, according to North London Press.
All council workers present in the office where the envelope was opened were taken to a separate room and quarantined for an hour while officers tested the powder.
An investigation by the Enfield Police is ongoing, and no arrests have been made.
"Communications of this type cause distress and upset to the recipient and also divert valuable emergency units away from those in genuine need of assistance," Enfield Police Sgt. Kevin Hughes said, according to North London Press. "We are now taking steps to identify the sender of this item and will make every effort to place them before the courts."
The envelope was sent to the environmental department.
"We take a very dim view of people attempting to terrify and intimidate our staff and we will be fully assisting police in their efforts to catch the perpetrators so they can be swiftly brought to justice," a council spokesperson said, according to North London Press.