trb is right – maternity leave does not grant you immunity.
However, find me a company that is willing to go that route and I will show you a management team with very big balls and even bigger lawyers.
The reality is that women who are either pregnant or on maternity leave are afforded quite a lot of protection from redundancy simply through fear of a company falling fowl of legislation.
This issue is made more acute by the fact that there is no limit on how much you can get sued for if you are found to have discriminated on the grounds of a ‘protected characteristic’, whereas if it’s just plain wrongful or unlawful dismissal, then the limit is £50k.
You could actually claim that by not selecting someone because they are on maternity leave, that this is itself sexual discrimination against men because men could never, by virtue of their sex, be on maternity leave. That argument might be even more compelling if say you were an expectant father who was not afforded the same immunity, which is effectively the ‘convesation’ I ended up having when this happened to me last year. It didn’t change the outcome, but it did give me a better negotiation position.