The abbot of Ealing Abbey has resigned over a failure to investigate child sexual abuse allegations at a London school amid an escalating diplomatic row prompted by the papal nuncio’s reluctance to cooperate with a public inquiry.

The independent inquiry into child sexual abuse (IICSA) was informed on Friday that Dom Martin Shipperlee, who had been abbot since 2000 and taught at St Benedict’s School in west London, had given up his responsibilities.

His abrupt departure comes immediately after he appeared before the inquiry, answering questions about how he handled allegations of sexual abuse against monks and teachers at the school dating back decades.

Two senior monks and teachers, Andrew Soper and David Pearce, were jailed for a series of offences against pupils at the school. Soper, who was found guilty of 19 rapes and sexual offences at St Benedict’s, fled to Kosovo at one stage in an attempt to escape justice.

The public inquiry has written to the pope’s representative in Britain, the archbishop Edward Adams, asking him to disclose details of his handling of complaints about Catholic schools in England and Wales and specifically relating to investigations at Ealing Abbey and St Benedict’s school.

The papal nuncio has so far failed to comply and declined to comment about the requests. David Enright, a solicitor at the law firm Howe and Co who represents 18 victims of abuse by Catholic priests and monks, who are taking part in IICSA, has written to Theresa May asking her to expel Adams if he does not comply.

In a statement to the Guardian, the Foreign Office confirmed it was investigating the papal nuncio’s position. A spokesperson said: “The government takes the issue of child protection extremely seriously. We fully support the IICSA inquiry and are looking into this matter further.”

The inquiry was told on Thursday that the nuncio was consulting with his superiors in Rome. Downing Street has not yet commented on the diplomatic standoff.

Shipperlee’s resignation was announced at the child sexual abuse inquiry on Friday by Dom Christopher Jamison, the head of the Benedictine Order in England. “This morning I received a letter from Abbot Martin Shipperlee offering me his resignation with immediate effect as abbot of Ealing,” he said.

“I have been present for the Ealing hearings … and I was particularly listening to Abbot Martin’s own evidence and towards the end, he said: ‘My administration of safeguarding, as has been serially revealed, is of an insufficient standard.’ So in the light of what I heard and in the light of his own self-assessment, I have accepted his resignation.”

Enright said: “It came as little surprise that Abbot Shipperlee resigned as abbot of Ealing, following his two-day cross-examination regarding child abuse in Ealing. However, removing one cleric will do nothing to address the fundamental problems of child abuse in the Catholic church.

“The papal nuncio’s refusal to cooperate with the IICSA demonstrates a distain for this public inquiry and child protection in the UK; it cannot be allowed to go unchallenged. There are only three options for the nuncio: cooperate with the IICSA, face criminal prosecution or face expulsion from the UK. I have written to the prime minister calling on her to support the IICSA chair, Alexis Jay, in this matter.”

Richard Scorer, a lawyer at the London firm Slater and Gordon specialising in abuse cases, who represents former pupils at St Benedict’s, said: “The stalling by the Holy See is utterly unacceptable and completely hypocritical given Pope Francis’s public claims to want to root out the cancer of clerical sex abuse. The inquiry has done all it can. It seems only intervention by the prime minister can now progress this issue, and given Theresa May’s public commitments to the inquiry, this needs to happen.”

Referring to Shipperlee, he added: “This resignation is long overdue. It has been obvious for over a decade that this man is wholly unsuited to his role yet his resignation comes only under the laser beam of this inquiry. This simply proves that the Catholic church will only do the right thing under external pressure.”