One of the country’s most venerable educational charities faces a backlash after it declined to sever its links with a sex abuser, a decision that has bewildered his victim.

It has emerged that, following a vote, the Society of Antiquaries, which describes itself as “Britain’s oldest learned society concerned with the study and understanding of the material past”, is to allow Hubert Chesshyre to remain a fellow.

The move has dismayed the society’s council, which said the decision showed it needed to modernise.

The Independent Inquiry Into Child Sexual Abuse (IICSA) heard evidence that in 2015 Chesshyre was found to have sexually abused a teenage chorister over the course of three years in the 1990s. Earlier this year the Observer reported the revelation had put pressure on several renowned institutions with links to Chesshyre to sever their ties with him. These included the Institute of Heraldic and Genealogical Studies, whose trustees promptly removed him as vice-president.

But others, including the Society of Antiquaries, have stood by him.

Chesshyre, an expert on heraldry and genealogy who held a number of senior positions within the royal household, was subject to a “trial of facts”, which are held when the accused is deemed unfit to plead. Such trials do not result in a criminal conviction but the jury can find whether a person committed the acts of which they have been accused.

The court recognised Chesshyre had suffered a stroke and it was also suggested that he had dementia. As a result, despite being found to have committed the abuse, he was given an absolute discharge.

Following the finding, the Honours and Appointments Secretariat – which is overseen by the Cabinet Office – recommended forfeiture of his honours as a result of the IICSA’s revelation. But a majority of the society’s fellows who were present for the vote backed him.

Chesshyre’s victim, who has remained anonymous, told the Observer: “Following the Jimmy Savile revelations, and scandals involving public figures that came to light, organisations have quickly distanced themselves from people tainted by even a suggestion of wrongdoing.

“I therefore find it baffling that the fellows voted by a substantial majority to continue the fellowship of somebody who was found to have committed these acts. It makes me wonder whether Britain’s establishment has really learned anything at all.”

In a statement the society, which was founded in 1707, confirmed its fellows had considered a resolution from its council to remove Chesshyre from the fellowship. It noted that in “March 2019 the Independent Inquiry into Child Sexual Abuse published proceedings confirming Chesshyre was found to have committed two acts of gross indecency with a male minor” and said this had prompted a number of fellows to write to the society, a registered charity which received a royal charter in 1751, requesting Chesshyre’s removal.

It said the council “regrets that a majority of those present did not see fit to support the resolution” and said it would “consider further the implications of fellows’ decision to reject the resolution to remove Mr Chesshyre and recognises this case has shown the need to modernise the society’s statutes and governance procedures.”

The society said it would “continue to fulfil its charitable objectives, including by encouraging young people to become involved in its activities, in environments that are safe for them.” But it conceded that the scandal around Chesshyre made this remit more difficult, adding: “This makes the acts which Mr Chesshyre was found by the court to have committed particularly harmful.”