@SerendipityJane I did seek union advice but to no avail. At one point, there was an expectation - unbelievable though this sounds - that I would even write the reports for the Mother-of-Four.
I don't know the precise details, but it turned out that Mrs X had previously threatened the LA with legal action for failing to return her to her previous post after her fourth maternity leave. (My understanding is that there was a dispute as to whether she was entitled to a job in the same area at the same level or whether it had to be the same position in her old school.)
It was presented to me as "...and Mrs X will not be writing reports." There were two deputes in my classroom when this was dropped on me. (To be fair, they were doing the bidding of our HT - a father of five...)
At this point, I smiled sweetly and asked who was going to be writing her reports in that case? I vaguely recall referring to the amount of time for reports included within the Working Time Agreement. (As a PTC, I was supposed to have fewer reports to write than a classroom teacher, but I was also expected to check all the reports for my faculty.)
In the end, one of the deputes did them together with the Mother-of-Four. That was the only battle that I won.
As for the business of other members of staff getting time off for nativity plays and other primary school related activities - "First Day of Primary School" was one that one father had four times - that was something that I was aware of throughout my teaching career. These days off weren't official - they were all in the gift of the HT. As suggest, there's nothing to be done when it's not in writing. It doesn't sound like a lot, but it all adds up.
Something that staff were entitled to by law: if a mother had given birth during a holiday period, then there was an entitlement to take the missed maternity/paternity leave during term time.
The LA was supposed to buy in cover for that. In actuality, the school just assigned other staff to cover the classes. I recall being on my knees one time trying to keep on top of everything and then being given cover classes for someone in my faculty who had given birth during the holidays and was taking her 'missed holiday' in Tenerife during term time.
Another time, I finished up covering a couple of PE lessons (not my faculty) because a father was off on holiday with his wife and two children. Again, the second child had been born during a holiday period and the law allowed the father to have time off.
We did ask the union about the fact that the LA was forcing in-house staff to cover, but were told that nothing could be done to make the LA buy in supply staff.