Trading returned to normal at Tesco after a security alert forced 14 stores to close across the UK.
Police are investigating who is responsible for the "series of threats" that led to the evacuation to hundreds of thousands of customers.
Eyewitnesses claimed they had been told of a bomb scare, while reports ranged from a financial motive to threats by the animal rights lobby.
Saturday had been designated a 'national day of action' against Tesco by animal rights groups including Viva, who claim the store has been selling live turtles at outlets in China.
Officers from Hertfordshire, where the firm has its headquarters, said there was no link to any form of extremism but urged the public to remain vigilant.
They said: "Inquiries to identify those involved in a series of threats to 14 Tesco stores continue as affected stores have returned to business as normal. Each of the stores involved has been searched and given the all-clear and the company continues to work closely with the Constabulary.
"The public are asked to remain vigilant at all times. There is still no reason to believe that the incidents are linked to extremism of any kind."
Tesco said in a statement: "Staff at the affected stores have done a fantastic job during this period and have worked very hard to make sure the stores are fully stocked and ready to welcome customers as usual today. The police are conducting a criminal investigation and Tesco cannot comment further."
A company spokeswoman said that stores were "expecting to be trading as normal".
The alert closed stores in Dyfed Powys in Wales, Fife and Strathclyde in Scotland, Lancashire, Suffolk, Leicestershire, Humberside, Herefordshire, West Yorkshire, Nottinghamshire and London.
