ginkster,
The lack of depth to cover gaps is the issue, not the gender or religion (or any other aspect) of the person causing the gap.
It wasn’t my intent to intimate that, I’m probably not putting my argument forward clearly. Imagine a squadron of mixed sexes, once confirmed to be pregnant, the female loses her flying medical category and is confined to ground duties, post birth add maternity leave, it is a considerable time before they can assume flying duties (if they wish to). Whilst off flying duties, others have to pick up the slack (assuming there is capacity to do that), therefore the effectiveness of the squadron is reduced. For Air Traffic, Fighter Control and engineering, some of the exec roles are fundamental to the running of that org and you cannot parachute people in to fill easily. For eng, once pregnant, they are put onto light duties, not allowed to work with petrol, oils and lubricants, therefore someone has to cover the duties. Yes, males do out of areas (like all others), Career Managers try to send them at the end of tour, so that there is no disturbance to the losing unit. For a flying sqn, it is highly unlikely that someone would be sent as a individual augmentee mid-tour. I get your point about illness/compassionate leave, the issue is you cannot reasonably expect it to occur and is an inevitability of the human race.
I get your hope that one day the RAF will have more redundancy to cover this, however I think that is wholly unlikely as we do more (or as much as now) with even fewer.
Chewkw mentioned about religious insistence, I have seen this twice, not UK military, but another nation, who military refused to operate during a certain religious observance.