Two men arrested under the Terrorism Act have been freed without charge after a suspicious substance was identified as “non-hazardous” oil.
The men were held after police searched a Bristol flat and found two 25-litre (5.5 gallon) containers labelled as holding hydrogen peroxide.
The discovery had led officers to suspect a link to terrorist activities.
One of the men is from Afghanistan and in his early 20s, while the other is Somali and in his early 50s.
The substance in the containers at the flat in Stapleton Road, Easton, is thought to be vegetable oil.
Police said the Afghan man had been bailed in connection with allegations of possession of class A drugs, and theft.
The incident began on Wednesday night, when the man was arrested in the centre of Bristol on suspicion of a drugs offence.
In a follow-up search, police found the two containers, and the second man was arrested.
Forensic analysis by a Home Office scientist then found the substance inside the containers was an oil-based liquid which was not dangerous.
Police are still investigating how the containers came to be at the flat, and where they came from.
Avon and Somerset Constabulary’s Assistant Chief Constable Steve Mortimore said he believed the police response had been “entirely appropriate”.
“When we found two containers labelled with hydrogen peroxide, we clearly had to take that very seriously, and an intensive operation began to try to establish exactly what we were dealing with.
“As recent events in London and Glasgow demonstrated, the terrorist threat in the UK is very real, and it is important that everyone remains alert to that threat.
“I hope that the public will be reassured that Avon and Somerset Police is vigilant to the threat, and that the force is ready and able to act swiftly and effectively if any potential terrorist risk comes to light,” he said.
He said police would be meeting community representatives in the city on Saturday to provide them with a further full briefing.