During the campaign, a blackmailer identified by the pseudonym "Sally" sent letters to Tesco stores threatening to harm customers if his demands—for Clubcards, modified so that the holder could withdraw cash from ATMs—were not met.

Several months after the threat first came to light, "Sally" sent out several letter bombs, one of which was received and exploded in the face of the householder, causing her shock and minor injuries, while the Royal Mail intercepted several other packages, which had been held up because insufficient stamps had been put on them.

Police eventually mounted a surveillance operation on the postbox to which several of the extortion letters had been traced and identified "Sally" as Robert Edward Dyer.

Dyer was arrested in February 2001, over six months since the beginning of the extortion attempt, and charged with several offences, including nine counts of blackmail and one of common assault, of which he was found guilty in May 2001.

A number of similar extortion attempts against supermarket chains and other businesses and subsequent attacks on Tesco have since been compared to Dyer's campaign by the media.

The campaign began in August 2000, when John Purnell, director of security for Tesco, the United Kingdom's largest supermarket chain, was telephoned by a newsagent in Bournemouth who had discovered a copy of an extortion letter left on his shop's photocopier.

The letter demanded that Tesco give away Clubcards, modified for use in cash machines, with a combined value of £200,000 in the Bournemouth Daily Echo.

Tesco feared that if the extortionist was to go on radio and give the pin code, this could have been a huge financial risk.Tesco determined that they could let a handful of the cards be used, before stopping the rest of them.

In 1990, Rodney Whitchelo,[5] attempted to extort £4 million from H. J. Heinz Company by spiking jars of baby food with broken glass and caustic soda.

Tesco stated that a number of employees had been dismissed for misconduct or had left the company with a grudge, potentially making them suspects.

Police suspected that whilst 'Sally' was an individual, wanting to make money for themselves, it may also have been a large criminal organisation, such as an anarchist group.

Making enquiries with Royal Mail, police discovered that a fire had been reported in a postbox on Bradpole Road, Bournemouth.

[4] Using a portable X-ray machine to ensure that 'Sally' hadn't made a bigger device, the bomb disposal team scanned the packages, before disarming the parcels by hand.

"[4][7] ACC Lee added: "The reason for singling out the supermarket chain is at this time unclear and our inquiries into any motive are being investigated.

In 1990, Edgar Pearce, dubbed the "Mardi Gras bomber" by the media, used bombs in an attempt to extort money from Barclays Bank and Sainsbury's supermarkets.

Tesco's position was that they wouldn't pay any extortionist, but would consider their support to a police operation in 'paying money in a controlled fashion'.

[4] The letter contained a three-part cipher which allowed the police to communicate with 'Sally' in code through cryptic adverts in the Bournemouth Daily Echo.

Instead of having previously had to be vague in the paper, due to members of the public being able to read the adverts, police could now be clearer with their communications, as only they and 'Sally' had the cipher.

[1][4] After being unable to identify 'Sally' on the surveillance footage, police placed another message in the Bournemouth Daily Echo, asking whether 'Sally' would accept a money-drop instead of collecting the money through ATMs, as it was 'technically impossible' to produce the cards.

Having lost patience, a letter stated that a pipe bomb would be placed in the garden of a Tesco customer if his demands were not met by 12 December 2000.

[4] Additional high-visibility patrols were put out in the area, including 'bomb cars' that could respond to calls from the public, in relation to suspect devices.

[4][5][6] The surveillance operation did not yield any results; instead Dyer spent most of his time visiting his elderly mother and carrying out errands.

[4] The police decided to confront Dyer and visited him at his home address, a two-bedroom bungalow in Caroline Road, Kinson, on 19 February 2001.

The letter was dated 15 February 2001 and reads as follows (with grammar and spelling mistakes adjusted): Without prejudice Do not understand mardi gra.

Sally[4]It was discovered that everything involved in the incidents, including the letter writing and bomb making, had been conducted by Dyer at his home address.

Within his shed, Dyer had made the devices and he had worn rubber gloves and used water, instead of his saliva, to put stamps on the letters, in an attempt to avoid detection.

[3][4] As Dyer's interviews continued, it was found that he had read the previous extortion cases that the police had identified, of Rodney Whitchelo and Edgar Pearce.

Recorder Christopher Clarke told Dyer: 'In August last year you embarked on an evil campaign of public extortion, intimidation and terror.

You planned your crimes with devious cunning and meticulous care', adding 'your sentence is intended to act as a deterrent to anyone else like you who may be tempted to follow the example of Witchelo'.

[4] DSI James later revealed that Dyer "was an individual in desperate need of money and believing that Tesco's were the answer to all his problems."