At the height of the Cold War, there seemed almost no limit to the appetite of the CIA to meddle in other countries. From industrial sabotage to political espionage, the agency’s clandestine web of influence stretched right across the globe. Even sport was sucked into this mania for intervention.

And the recent claim that the CIA secretly plotted to wreck the England football team’s bid to retain the World Cup in 1970 shows just how febrile a time it was.

According to conspiracy theorists, the scheme was brilliantly successful: England were dumped out at the quarter-final stage in Mexico after a bizarre mishap which drastically weakened their side and enabled Brazil to emerge as the ultimate winners.

As the story goes, soon after England’s unexpected, premature exit, British football writer Bob Oxby visited Washington to see his cousin, Stuart Symington, the long-serving Democratic Senator for Missouri who had deep connections with US intelligence.

Inevitably, the subject of England’s defeat came up in conversation. ‘That was the CIA!’ exclaimed Symington, who was regularly briefed about covert operations.

At the heart of the alleged plot was the determination to force the withdrawal of England’s legendary goalkeeper Gordon Banks by poisoning his food or drink. Banks was targeted because his world-beating brilliance made him the keystone of the team: pull him out and the whole structure would collapse.

Indeed, that is exactly what happened. On the eve of the quarter-final, against West Germany in the city of Leon, he was mysteriously struck down by a violent stomach upset. ‘This was no normal tummy bug. That night I spent more time sitting on the loo than I did lying in bed,’ he later recalled.

His place was taken by Chelsea goalkeeper Peter Bonetti, known as ‘the Cat’ because of his agility. But he gave a dog’s dinner of a performance as a result of his jangling nerves, conceding three goals as West Germany won 3-2.

‘I still can’t believe it. Of all the players to lose, it had to be him,’ said England manager Sir Alf Ramsey, referring bitterly to Banks’s absence. 

Banks himself always thought he had been ‘nobbled’. The same whispers circulated in the press box. Brian Glanville, the respected newspaper correspondent writing in 2007, said: ‘I have steadily come to believe that Banks was the victim of sabotage.’

England embark on a new World Cup campaign this month – with Mexico again featuring as one of the hosts – and the story of the CIA plot has been given new salience by a podcast made by investigative journalist Gabriel Gatehouse and Gordon Banks’s own grandson, Ed Jervis – who is convinced his grandfather was the victim of a deliberate poisoning.

While the CIA scheme may seem outlandish, Gatehouse says the rationale for the agency’s action can be found in the political landscape of Latin America, which in the 1970s was a proxy battleground for the titanic clash between the Soviet bloc and the West.

Keen to create a bulwark against the spread of communism, President Lyndon Johnson’s White House had, in 1964, helped install a Right-wing military dictatorship in Brazil through General Emilio Medici.

Six years later, the general’s regime was fading. In this football-mad country, the obvious way to rebuild public support would be World Cup glory – and that meant clearing England off the road.

Within the US government, there was also animosity towards Labour prime minister Harold Wilson, because of his refusal to become involved in the Vietnam War. A slippery opportunist, Wilson had just called a general election in the hope that Labour could capitalise on the expected progress of Sir Alf’s team.

But the move backfired disastrously, with Bonetti’s collapse in the penalty box soon followed by Wilson’s flop at the ballot box.

In addition to the motive, the CIA certainly had the means. Over the decades, the agency had built an impressive arsenal of poisons, biological weapons and toxins, while its technicians were at their most ingenious in developing new devices for taking out Cuba’s leader Fidel Castro. These included an incendiary clam shell, a poisoned wet suit, exploding cigars and a lethal milkshake.

Yet this is not proof of a CIA plot against Banks. Gatehouse and Jervis can produce no hard evidence to back up their case. In truth, their whole argument is riddled with gaping holes.

One of their biggest is the claim that Banks must have been singled out because no other England player became ill. But that is simply untrue. According to the notes kept by team doctor Neil Phillips, at least four other players – Bobby Charlton, Peter Osgood, Keith Newton and Alex Stepney – were struck down by the bug.

To protect their health, the squad also had its own chef, while Sir Alf negotiated with the Findus company to import vast amounts of food and drink to Mexico.

For Sir Alf, the strength of these precautions added credibility to the plot theory. As he put it to sportswriter Nigel Clarke: ‘It may have been done by the CIA... I know Gordon was got because we brought our own water and food.’

Banks was no rebel and his family maintains he complied with all of Sir Alf’s rules. But that is not the whole story.

When researching a biography of Sir Alf, I interviewed the team doctor Neil Phillips and he told me of his annoyance that all the good work on safety had been undermined by a group of players – among them Banks and Charlton – having a small party in one of their hotel rooms to celebrate a group stage victory over Czechoslovakia. Surprisingly, Sir Alf gave permission for the gathering, but Phillips disapproved and his worst forebodings were fulfilled.

Soon after the World Cup, Phillips had a talk with Leeds manager Don Revie, who had been out in Mexico as a pundit. ‘Don said to me: “Neil, never blame yourself for what happened out there. The players, contrary to your instructions, were having sandwiches delivered to their rooms. 

'I know what you had told them – no drinks or sandwiches in the rooms. You can take it from me, Neil, that some of them had room service.”’

This ill-judged event, rather than a CIA plot, is the real explanation for Banks’s illness. The 1970 England squad was neither as cohesive nor as disciplined as the 1966 team, failings that were epitomised by divisions over the presence of wives and girlfriends.

The majority were unaccompanied, but four players brought their partners, who became something of a distraction.

As Phillips told me: ‘When the players were trying to ring their wives, the others would take the mickey out of them. “Oh, they’re still in bed,” or “they’re swimming nude in their hotel pool, having a whale of a time – why would they want to speak to you?” 

'It was all jocular stuff. But it showed the 18 players in the squad without their wives were not happy with the other four.’

The uxorial problem was at its most acute in the case of Peter Bonetti. A devout Roman Catholic, he was gripped by anxiety about his wife’s rumoured infidelity. 

Brian James, the distinguished Daily Mail football correspondent at the time, told me: ‘Frances Bonetti was very, very pretty but she was one of those girls who used to come on to everybody. I think it was just her nature. Peter was very upset when he heard people talking about his wife. On the night before the big match, he was tearing round looking for her.’

The tale of a CIA plot might superficially sound impressive, but it is a story built on sand.

Banks’s own German-born wife, Ursula, whom he met while on National Service in the mid-1950s, was also unimpressed by the theory. As her granddaughter put it this week: ‘She didn’t take much nonsense.’