THE Times was among the newspaper offices across the country sent warnings of a bomb threat to Tesco stores last weekend. The letter was opened by general manager Lyn Roberts on Monday morning but referred to an incident at the New George Street store in Plymouth which had been due to happen on Saturday, July 14. Fourteen stores were closed on Saturday following a series of threats, and on Monday bomb disposal teams carried out a controlled explosion on a suspicious package at a Tesco store in Bristol ?as a precaution?. The letter to the Times stated that between 2pm and 7pm on Saturday, July 14 an explosive device would detonate at Tesco supermarket, New George Street, Plymouth. It also asked the recipient to inform the authorities to ensure minimum loss of life. Mrs Roberts said she believed the letter must have arrived on Saturday morning when the office was closed. ?It was a computer generated letter on a scrappy piece of paper,? she said. ?I immediately took it down to the police station.? The Tesco store in Launceston was also threatened in a letter opened on Monday morning by another local newspaper. The letters and envelopes are being forensically examined by the police. PC Baxter Provan from Devon and Cornwall police said Hertfordshire police were taking the lead in the investigation: ?Letters were received across Devon and Cornwall and we will be liaising with colleagues from Hertfordshire about this,? he said. ?Some of the letters arrived after the threat date but it is possible they were held up in the recent postal strike.? Reports have suggested the letters may be financially motivated or linked to animal rights. Saturday was designated a national day of action against Tesco by animal rights groups. PC Provan said Herfordshire police were not linking the threats to extremists. Tesco stores that were closed on Saturday following the security alert were either re-opened that evening or on Sunday morning. Neither the New George Street store or the Launceston store were closed after the letters were received on Monday. A Tesco spokesman said: ?Tesco is aware that media organisations found threats after the weekend relating to possible incidents at stores in their areas during a specified period on July 14. ?Staff at the affected stores have done a fantastic job and worked hard to make sure stores were fully stocked and ready to welcome customers as usual.? He said staff safety was paramount at all times.