Simon Case, the head of the civil service, has returned to the Garrick six months after his high-profile departure, and is understood to be among a number of members whose resignations have been withdrawn by the club’s management.

Case quit the Garrick in March after the Guardian published the names of about 80 senior politicians, lawyers, leaders of arts organisations and actors who were members of the then men-only club, which until this year was notorious for rejecting proposals to admit women.

A club vote in May acknowledged that women could become members, but it has subsequently elected only two women – the actors Dame Siân Phillips and Dame Judi Dench – to join the 1,500 men listed in its membership booklet.

Case announced this week that he would step down from his job as cabinet secretary at the end of the year on health grounds. In his role, he is the leader of half a million civil servants and has been responsible for improving diversity.

At the Garrick there appears to be an internal reluctance to speed up the admission of more women in significant numbers despite the change of policy. Only about a dozen women have been nominated as potential future members and the admissions process means it usually takes several years for new people to be approved.

An article in the latest edition of the club magazine headlined “No fast track”, written by the chair of the club’s candidates’ committee, states: “As the chairman has made clear, there will be no ‘fast-tracking’ of women members except in exceptional circumstances.”

Case was criticised when his membership of the-then all-male club became public knowledge. Asked during a select committee hearing in March how he could “foster a genuine culture of inclusiveness” within the civil service while being a member of the Garrick, he initially defended his membership, stating he was committed to reforming it from within, before deciding 24 hours later to resign from the institution, which had been men-only since it was founded in 1831.

The club’s membership list includes the king, several high court judges, politicians, heads of several publicly funded arts institutions such as the Royal Opera House and the Royal Ballet School, directors of publishing houses, dozens of senior lawyers and leading actors including Hugh Bonneville, Benedict Cumberbatch and Matthew Macfadyen.

The club’s management is understood to have allowed members who resigned in March and April amid publicity over the no women members policy to withdraw their resignations and resume their memberships without needing to go through a lengthy and expensive official rejoining process.

One member who resigned amid the controversy over the men-only rules said his resignation was never formally processed because of the speed with which the club moved to clarify that women were in fact allowed to join.

Another member who resigned said the club allowed people who had left the club in March and April amid unease about the publicity over the club’s men-only status to “withdraw their resignations because there hadn’t been time for the regular committee meeting to take place to formally accept them”.

A Cabinet Office spokesperson said Case resigned his membership earlier this year as reported at the time, and had previously campaigned within the club for a change of membership rules; the spokesperson was not able to comment on whether Case has subsequently rejoined the club. The MI6 chief, Richard Moore, who resigned at the same time as Case, is understood not to have returned to the club and nor to be intending to rejoin.

Prof Rosie Campbell, the director of the Global Institute for Women’s Leadership at King’s College London, said she was disappointed by Case’s decision. “Staying a member when just two women have joined and when there will be no fast-tracking of more women signals a lack of sincerity in the original resignation. When Case was asked about the Garrick at a select committee, he joked about it as if it wasn’t a big deal – he clearly didn’t understand the deeply felt concerns of women in the civil service and what this said about his commitment to equality.”

Jill Rutter, a senior fellow at the Institute for Government, said: “Progress will be very slow unless clubs take special measures to accelerate entry of people who’ve been excluded and current members will need to judge whether they are comfortable with that.”

The fallout from the Garrick’s decision that women should be admitted as members continues to ripple through a dozen remaining men-only clubs in central London.

Last week, the Savile Club, founded in 1868 by writers and artists, held an informal meeting of members who favour the admission of women; a second meeting organised by members who do not wish to admit women is set for late October. The 140-year-old Flyfishers’ Club is due to decide on Friday whether women should be allowed to join after protests from some of Britain’s most high-profile female anglers.

The Garrick was contacted for comment.