Fourteen Tesco stores across the UK have been closed by police following a series of threats.
Reader James Collins photographed a shut Tesco in Kirkcaldy, Fife
Police have launched a criminal investigation but say they do not believe there is a link to extremism.
Hertfordshire Constabulary, which is leading the investigation, said the stores were closed as a precaution and no-one had been hurt.
One of the stores has since reopened and Tesco says all the others will be open again by Sunday morning.
Tesco stores were closed at Port Talbot, south Wales, Pontefract, West Yorkshire, and Market Harborough and Ashby de la Zouch, Leicestershire.
Other branches shut were in Bury St Edmunds, Suffolk; Hucknall, Notts; Hereford and Ledbury, both in Herefordshire; and Barnes, south west London.
The last of these was the first to be reopened on Saturday evening.
Scottish branches of the supermarket were also closed in East Renfrewshire and Fife.
Police said other stores were closed in regions covered by their forces in Lancashire and Humberside.
Darren, an employee from the Ashby de la Zouch store said staff were told to evacuate the shop.
"We were allowed to go back in to get our belongings," he said. "We had to be as quick as we possibly could.
A reader sent in this picture of the deserted Tesco store in Port Talbot
"We were informed briefly that the store was going to be closed for the rest of the day and we could go home straight away."
The Tesco store in Barrhead was closed at about 1230 BST on Saturday.
Police initially closed off the car park leading to the store and several other neighbouring shops, but it was opened within an hour.
A worker at a nearby shop said police had told him the store had been shut after receiving a bomb threat, along with several other supermarkets across the country.
Martin Jacklin was shopping in a Tesco store in Hucknall, Notts, when shoppers were told to take their shopping to the tills and leave at about 1415 BST.
He said: "Me, the wife and the children were in there, basically just doing a normal shop and it came over the tannoy that we were asked to leave, basically, go to the cashier, pay for your groceries and then leave.
"It was quite smoothly done. We spoke to a woman outside who worked there, she said she was just told to leave, not even to clock off, just to go."
A spokeswoman from Hertfordshire Constabulary said: "Police in Hertfordshire have launched a criminal investigation following a series of threats made to 14 Tesco stores across the country."
The force is leading the nationwide investigation because the retailer has its headquarters in the county.
The spokeswoman continued: "While the public are advised to remain vigilant we have no reason to believe that the incidents are linked to extremism of any kind.
"Every effort is being made to trace those involved."
Tesco is believed to have lost millions of pounds worth of business as a result of the closures.
A Tesco spokeswoman said: "Tesco is working with the police following a series of incidents.
"Police are investigating and so we are unable to comment further."
She added: "As always, customer welfare is our priority."