A former tax inspector who admitted targeting Tesco in a £1m blackmail plot has been jailed for six years.
The closures cost Tesco an estimated £1.4m in lost revenue
Philip McHugh, 52, from Clitheroe, Lancashire, demanded £500,000 from the supermarket giant twice last year.
He sent 76 letters threatening to bomb stores and contaminate products if the Hertfordshire-based firm refused to comply with his demands for money.
His threats resulted in 14 stores across the UK closing last July as a security precaution.
The judge at St Albans Crown Court said McHugh was guilty of a sustained and serious effort to extort money from the chain.
He pleaded guilty last year to three sample charges of blackmail and two of communicating a bomb hoax targeting the retailer.
The campaign started last May when McHugh sent a series of letters to Tesco offices in Dundee, threatening to contaminate food unless he was paid £100,000.
When this failed McHugh, who was addicted to online gambling and had debts of £37,000, sent a series of increasingly threatening letters to Tesco's headquarters in Hertfordshire.
He said he would put caustic soda in yogurt sold in the store if Tesco did not transfer £200,000 into his bank account.
When this also failed, he sent hoax bomb warnings to 76 Tesco supermarkets, warning bombs would go off in the stores on 14 July, which he called "Black Saturday".
On this date stores were evacuated and temporarily closed in Port Talbot, south Wales; Pontefract, West Yorkshire; Market Harborough and Ashby de la Zouch, Leicestershire; Bury St Edmunds, Suffolk; Hucknall, Nottinghamshire; Hereford and Ledbury, in Herefordshire; Barnes, south-west London, and in East Renfrewshire and Fife.
The other closures took place in regions covered by the Lancashire and Humberside police forces.
The closures cost the chain an estimated £1.4m in lost revenue.
McHugh wrote to the executives of the supermarket chain following the bomb hoaxes demanding £200 a day, and an overall figure of £1m.
He wrote: "I'm absolutely desperate and blood will flow if you do not co-operate."
McHugh signed his letters "Arbuthnot, the sign is the spider"
"And I WILL destroy your business and others will pick up your customers."
McHugh set up a bank account to receive the money, but it only allowed him to withdraw £200 a day.
At that rate it would have taken more than 13 years to withdraw the full sum.
McHugh suffered severe depression in the months leading up to his campaign, and told a psychiatrist he saw the blackmail attempt as a "last gamble" at getting his life back on track.
Detective Chief Inspector Bill Jephson, of Hertfordshire Constabulary, which led the investigation, said McHugh was a desperate man, without any means to make money.
He said: "He didn't think twice or even care about the possible consequences of his actions. He became fixated and enjoyed the thrill of blackmailing Tesco."