The downfall of Sepp Blatter and the disgraced Fifa president’s one-time heir apparent, Michel Platini, is all but complete after both were banned from football for eight years by the world governing body’s own ethics committee.

Both men were cleared of corruption charges but found guilty of a series of other breaches including a conflict of interest and dereliction of duty over a 2m Swiss francs (£1.35m) “disloyal payment” from Blatter to Platini, the Uefa president, in 2011.

While they will fight to clear their name at Fifa’s own appeals committee and the court of arbitration for sport, the verdict looks likely to finally bring the curtain down on Blatter’s controversial 40-year tenure at Fifa and Platini’s hopes of replacing him in the top job.

A defiant but visibly weakened Blatter, so used to being the centre of attention, immediately held a press conference in Zurich in which he referenced Nelson Mandela and the Nobel peace prize. “I am not ashamed,” said the 79-year-old Swiss. “I am sorry that I am a punching ball. I am sorry for football … I am now suspended eight years. Suspended eight years for what?”

Platini, who worked at Fifa from 1998 to 2002 and has been Uefa president since 2007, said the decision was a “pure masquerade”. “It has been rigged to tarnish my name by bodies I know well and who for me are bereft of all credibility or legitimacy.” Uefa said it was “extremely disappointed” with the decision.

It was hard to escape the impression that Blatter had been undone by the very tools he had often used to control and expel his enemies during his 40 years at Fifa, 17 of them as president. Like Platini last week, he intimated the ethics committee had an ulterior motive in banning him on grounds that he said were unfair.

Fifa was thrown into crisis in May when Swiss police raided the five-star Baur au Lac hotel and nine senior football officials were indicted in the US on charges including money laundering and racketeering. Last month, a further 16 individuals were charged after more early morning raids.

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Under huge pressure, Blatter agreed to stand down a few days after being re-elected for a fifth term as president in May. Platini quickly emerged as the favourite to succeed him, much to the public chagrin of his erstwhile mentor.

Blatter appeared personally before the ethics committee last Thursday, protesting his innocence in a letter to all 209 Fifa members in which he likened the process to the Spanish inquisition. Platini refused to appear in person, with his lawyers taking part in the nine-hour hearing on his behalf.

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But neither man has been able to provide a written contract for the £1.35m payment or definitively explain away why it was eventually paid in 2011, a few weeks before a presidential election at a time when Blatter was facing a challenge from Mohamed bin Hammam, the Qatari who himself was ultimately banned from football over bribery claims.

Platini acted as a special adviser to Blatter from 1998 to 2002. The Frenchman has claimed Blatter told him at the time that Fifa could not afford to pay him, despite the governing body making £78m over that four-year cycle, and did not want to break its wage structure. Blatter and Platini have said they believed their verbal contract was legal under Swiss law. However, Swiss law places a five-year time limit on such payments.

In addition to alleged corruption, which carried a potential lifetime ban, the charges were based on four other potential breaches: mismanagement, conflict of interest, false accounting and noncooperation with the ethics committee.

Facebook Twitter Pinterest Blatter has plenty to ponder. Photograph: Walter Bieri/AP

The judges said: “Neither in his written statement nor in his personal hearing was Mr Blatter able to demonstrate another legal basis for this payment. By failing to place Fifa’s interests first and abstain from doing anything which could be contrary to Fifa’s interests, Mr Blatter violated his fiduciary duty to Fifa. His assertion of an oral agreement was determined as not convincing and was rejected by the chamber.”

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Platini, the ethics committee judges said, also placed himself in a position of a conflict of interest and violated his fiduciary duty to Fifa. “Mr Platini failed to act with complete credibility and integrity, showing unawareness of the importance of his duties and concomitant obligations and responsibilities.”

Blatter acknowledged an administrative error in failing to register Fifa’s debt to Platini in its accounts for eight years, though he insisted: “This is nothing to do with the ethics regulations.”

Blatter, accompanied by his daughter, Corinne, tried to summon his usual defiance in insisting he was still the Fifa president and declaring: “I’ll be back,” as he took his leave.

“I have never cheated with money,” he insisted. “I am still the president. Even if I am suspended, I am still the president.”

But he was a much-diminished and frailer figure than the one who stood on stage in a Zurich conference hall days after US prosecutors had indicted nine senior Fifa officials among 14 football executives charged with money laundering and corruption offences.

Sporting a large plaster on his right cheek following minor surgery to remove a mole last week, he said that a health scare at the beginning of November would have killed him had it not been for his doctors.

Eight months after he won an election to consolidate his reign as Fifa president for another four years, Blatter still insisted he would return to oversee the Fifa congress in February that will decide his successor. But his chances of making his departure in the manner that he envisioned in front of Fifa’s 209 members – many of whom still support him – now hang by the slenderest of threads.

Platini’s demise was, if anything, even more swift. Having pledged reform to heal Fifa’s tattered reputation and demanded that Blatter stand down, the French Uefa president quickly emerged as a strong candidate to succeed him.

Despite questions over his earlier links to Blatter and the manner in which he backed Qatar’s 2022 World Cup bid, he was a clear favourite until Switzerland’s attorney general launched an investigation into what Swiss law terms a “disloyal payment” and the Fifa ethics committee followed suit.

Damian Collins, the Tory MP who plays a key role in the New Fifa Now campaign group, said: “The fish rots from the head down and we know how rotten the head of Fifa was.”

But within the dysfunctional football family that will supply Blatter’s successor unless campaigners succeed in forcing external reform, there was sympathy for his plight. The former Asian Football Confederation general secretary Peter Velappan said: “This is very harsh, especially for Blatter because he dedicated his life to football and Fifa. Eight years is like a death sentence.”

Sheikh Salman, the Bahraini president of the AFC, is favourite to succeed Blatter. He said in an interview last week that the series of US arrests that precipitated the current crisis were “nothing to do with Fifa”.