Trading has 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 saw hundreds of thousands of customers evacuated on Saturday afternoon.

Tesco has remained tight-lipped over what caused it to close its doors at stores including one in Barrhead, East Renfrewshire.

There were claims of a bomb scare, while reports ranged from a financial motive to threats by the animal rights lobby.

Saturday was 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 extremism but urged the public to remain vigilant.

As well as Barrhead, the alert closed stores in Fife, Dyfed Powys in Wales, Lancashire, Suffolk, Leicestershire, Humberside, Herefordshire, West Yorkshire, Nottinghamshire and London.