Fifty years ago, betting at greyhound tracks was organised through a primitive computer called the Totalisator.

The "Tote" added up how much money was bet on each dog in a race, and calculated the odds, ensuring lucky punters a fair return.

In 1961, off-course gambling was legalised in Britain. Betting shops opened in every High Street.

Off-course bookmakers took bets on dog races at Tote odds, usually covering the risk themselves. But if a betting shop received a surge of money on a particular greyhound, it could phone in to the stadium, effectively hedging its bets by feeding its data into the overall Tote calculation.

A greyhound enthusiast from the Oldchurch area of Romford spotted an opportunity. I'll call him Mr Whippet.

Tote odds were finalised just before a race. As greyhounds were led to the traps, experienced punters at the track rushed to back the friskiest dogs.

Mr Whippet realised that if Tote odds at the track could be made to favour some bow-legged mutt with no chance of winning, bets placed on healthy hounds at remote locations might harness a bumper return.

He found backers to finance a scheme that required cash, military precision and total secrecy.

On June 30, 1964, six dogs ran in the 4.05 afternoon race at Dagenham greyhound track, then a subsidiary of Romford Stadium.

Two of them were fancied runners, two were outsiders, two were no-hopers.

On the two fancied runners, non-Tote bookies offered 2 to 1 against Buckwheat and 9-4 against Handsome Lass. These two did indeed run home first and second. On a non-Tote combination bet, you'd get odds of something like 9-2.

Mr Whippet insisted that it was not trickery but his knowledge of dogs that lay behind the "Dagenham Coup". He recruited no fewer than 170 men, organised into two groups.

Shortly before the race, the first group crowded the 31 Tote windows at the Dagenham track, blocking genuine punters. They bet heavily on the two no-hoper outsiders, forcing their odds down, thus making the other four runners an attractive proposition.

Romford Recorder: And they're off... racing greyhounds leave the trapsAnd they're off... racing greyhounds leave the traps

Meanwhile, just minutes before the race, at betting shops around Britain, men from the second group put money on various combinations of the other four dogs.

At a crucial moment, unknown persons – their identities were never established – sabotaged the stadium's phone lines. With the telephones suddenly gone dead a few minutes before the race, off-course bookies and betting shops were prevented from feeding their bets into the Dagenham Tote, and so overcoming the distortion in the odds.

Only one ticket for Buckwheat and Handsome Lad was sold at Dagenham, but the combination was heavily backed off course. A two-shilling (10p) stake stood to win over £987.

Over 300 similar wagers had been placed around Britain. If the betting shops paid at track odds, anyone who bet on Buckwheat and Handsome Lass would net, not 9-2, but over 9,200-1. Bookmakers faced losing a fortune.

The syndicate's gains would more than cover all the 11,000 wasted bets they'd placed to influence the odds. Profits were estimated at £600,000 – millions in today's values.

The bookmakers refused to pay. They sued the Romford Stadium Company, Dagenham's owners, claiming it had failed to safeguard its Tote operation. They also went after Mr Whippet and his backers, alleging unlawful practice.

Because nothing like the Coup had ever happened before, the law wasn't clear. In 1966, a judge turned himself into an arbitrator. He told Romford Stadium to pay the bookies' legal costs. This huge bill forced them to sell their Dagenham operation, which closed.

Mr Whippet was allowed to collect on the one winning ticket. The judge advised betting shops to refund all bets, but to take pity on genuine punters – their own regular customers – if they had winning tickets.

Mr Whippet unsuccessfully demanded that the bookmakers lose their licences for failing to honour their bets. Nobody was prosecuted for slashing the phone wires.