The Fifa president, Gianni Infantino, and secretary general, Fatma Samoura, were accused of “violating the norms and standards of good conduct” by a governance committee member who resigned, alleging they had improperly interfered with a decision.

Navi Pillay, a renowned International Criminal Court judge and former UN High Commissioner of Human Rights, accused Infantino and Samoura of “undue influence” in her letter of resignation from the governance committee after its chairman Miguel Maduro was replaced without notice in May. Maduro told the House of Commons select committee for culture, media and sport on Wednesday that Infantino and Samoura had interfered and pressured him to change a decision to bar the Russian deputy prime minister, Vitaly Mutko, from standing for the Fifa council.

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Maduro said Samoura argued the World Cup next year in Russia would be “a disaster” if Mutko were excluded and that as a consequence Infantino “feared for his presidency”. Maduro and the committee maintained their decision that Fifa’s rules requiring political neutrality did not allow a serving minister to be on the council. He said in parliament that Infantino had chosen “political survival” as the Fifa president, instead of properly maintaining the organisation’s independent reform structures following a deluge of corruption scandals.

In her resignation letter to Samoura, published by the parliamentary select committee on Thursday, Pillay wrote: “I wish to draw your attention to the prohibition, in the rules, of improper interference, exercise of influence or pressure, and the need to disclose these approaches, if we had been subjected to them, rather than maintaining secrecy.

“In compliance with this regulation, the facts of undue influence exerted on the Chair to change a recommendation made by the [governance committee], were made known to me.”

Written on 17 May, a week after the Fifa council summarily ended the tenures of Maduro and the ethics committee chairmen Cornel Borbely and Hans-Joachim Eckert, Pillay continued in her letter: “As a judge and former UN High Commissioner of Human Rights, I adhere to principled conduct at all times; and cannot countenance serving in an institution, whose officials violate the norms and standards of good conduct, that they themselves adopted.”

Her strident criticism supported that of Maduro, who argues that Fifa has a “deeply embedded” culture, derived from self-interest and lack of governance, which makes it resistant to independent scrutiny, transparency and accountability.

Pillay concluded that she lacked confidence in the future governance at Fifa, stating: “I remain concerned that the [governance committee]’s independent functioning will not be respected.”

In a telephone conversation from her home in Durban, Pillay told the Guardian the involvement of other distinguished figures made her believe Fifa were serious about reform. There was added significance for her, she said, because of the criminal allegations made by the US Department of Justice that South Africa’s bid to host the 2010 World Cup had paid $10m in bribes – which the bid officials and government have denied.

“I went in with great admiration that Fifa had adopted good principles, but they didn’t even consider who we, people with some background in this work, and they rode roughshod over us,” Pillay said. “You cannot just have reform as rhetoric and carry on with the old ways. That is where the rots sets in, when you violate the rules yourself.”

Another of three governance committee members who resigned, the New York University law professor Joseph Weiler, has complained to Fifa’s ethics committee, alleging improper influence by Infantino and Samoura.

The English Football Association’s representative on the Fifa council, David Gill, approved the replacements of Maduro, Eckert and Borbely at the Fifa congress in Bahrain. He and the FA declined to comment following Maduro’s evidence in London.

Fifa responded to Maduro’s accusations by saying it was “normal” for officials to be in regular contact with him: “Exchange between the administration and Fifa’s committees, which in the end all defend Fifa’s interests, are logical and even desirable,” Fifa said in a statement, “so for these exchanges to be portrayed as undue influence is factually incorrect.”

But Maduro responded strongly to that, noting that Fifa did not contest that the exchanges with Samoura and Infantino had taken place, saying: “The fact that they don’t see anything wrong with what I portrayed is the strongest confirmation of how deeply embedded is the culture I described. Genuine reform will only come about from the outside.”