The resignations of two of Britain’s most senior Whitehall figures from the men-only Garrick will prompt difficult questions for dozens of other powerful individuals from the UK’s male-dominated establishment who remain members.

Neither the cabinet secretary and head of the civil service, Simon Case, nor the head of MI6, Richard Moore, resigned in a particularly dignified manner.

Initially, both seemed to think that the Guardian’s revelations about their membership merely required a skilful bit of news management from their media advisers. Both concluded there was no pressing need to resign from the central London club, with its billiard room, libraries, bars and multiple dining rooms, staffed by waiters in pristine white jackets.

However, within 24 hours of announcing to colleagues that they would not be resigning, both made a U-turn and let it be known that they would after all be giving up their membership of a club that has courted controversy since the 1960s because of its refusal to admit female members.

Moore sent a long email to staff on Tuesday morning after the Guardian’s first article naming him as a member, explaining that he had tried to resign from the club last year, when controversy over the club’s sexism problem surfaced once again (as it has done periodically for decades), but had been persuaded by the club’s chair to stay until a new vote on the matter, planned sometime this year. He is understood to have admitted to staff in that first message that his membership of the club was a bone of contention even within his family, and to have made a commitment to colleagues that he would not use the club socially until the ban on female members was lifted.

This email did not satisfy colleagues. Moore’s decision to resign is understood to have come after several discussions with an internal group, Women in Secret Intelligence Service, who shared their disappointment over his membership of the club with him. The issue has clearly been sucking up a lot of time that MI6 might otherwise have been spent working on what their website cites as their “three core aims: stopping terrorism, disrupting the activity of hostile states, and giving the UK a cyber advantage”.

He sent an updated message to staff on Wednesday morning letting them know that he had reflected on his earlier decision, and resigned because he did not wish to risk attracting continued focus on the issue by the press when the service was in the middle of a concerted drive to attract more female staff.

Case’s resignation followed an equally messy trajectory. For a brief reminder of what the British male establishment sounds like, it is worth taking a minute and a half to listen to the guffawing and bellowing audible in a clip from Case’s appearance at the cross-party liaison committee hearing in the House of Commons on Tuesday afternoon.

Case, the head of the civil service, was asked by the Labour MP Liam Byrne whether it was possible to “foster a genuine culture of inclusiveness” within the civil service while being a member of the Garrick. He tried to laugh the question off, before telling the committee (made up of six male MPs and one female MP): “If you believe profoundly in reform of an institution, by and large, it’s easier to do if you join it to make the change from within rather than chuck rocks from the outside.”

The Conservative MP Robert Buckland said “hear hear” to Case’s comments, before saying that he wished to declare an interest and revealed that he too was a member of the Garrick. This prompted huge, gusty male laughter from some of the other men around the table. It is hard to see precisely from the video clip, but it looks as if the man next to Buckland slapped him on the back affectionately.

When the Conservative MP Harriett Baldwin asked what the Garrick was, she was told firmly and patronisingly by the committee chairman, Bernard Jenkin: “It’s not very important.” There was more cheerful laughter and Case looked relieved, as if he had dodged a bullet.

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However, less than 24 hours later, Case appears to have decided that the matter was in fact important. His defence, that he was heroically attempting to reform from the inside, has attracted much ridicule online, where people have asked whether he was also planning to join clubs known to be racist in a bid to promote change from within.

Critics have made it clear that their unease with membership of the Garrick is not just about the club’s refusal to admit women, but also its wider lack of diversity.

Hannah White, director of the Institute for Government, an organisation that works with MPs and senior civil servants to make government more effective, said: “If you look down that list of names that have been published, it is incredibly un-diverse on a multiple different fronts. People who are minoritised in various different ways will look at it and think: that is a group of older white men – so what we always suspected about how older white men get together to run the country is likely to be true.”

Senior female judges have expressed anger at the concentration of judges who have continued to be a member of the club, in the face of years of campaigning for them to resign. These developments may prove thought-provoking for 1,500 people whose names are listed in the Garrick’s small grey membership book.