"Consultation etc - yes of course but in reality I've found that consultation doesn't change the basic fact that, provided the reason is legitimate and the due process has been followed, an employer can change T&Cs, including the handbook, and there's not much an employee can do about it."
You are not wrong, but that's surely not a reason to advise someone that no process is required? It sounds like in the OPs case due process hasn't been followed, so telling the OP her employer was only required to give sufficient notice of the change could (had she chosen to believe your advice to be accurate) have led her not to challenge her employer's actions, believing them to be entirely legitimate.
Many employers who try to get away with changing something without due process and consultation will back down if challenged, not wanting to go through a difficult consultation process or terminate people's employment.
There's a difference between wanting to do something because it would be better for the business and absolutely having to in order for the business to survive. If the business reason for this change is nearer the "it would be better for the business" end and not actually completely critical, it's perfectly possible they may back down rather than terminate the employment of someone on maternity leave, which any sensible employer would only do if unavoidable.
Sorry, it's just a bugbear of mine. It irritates me when people state authoritatively that x is definitely the case, thus giving the impression that they have expert knowledge, when they are wrong. I think I'm just very conscious that I know for a fact that lots of people have acted on the basis of what I've said on these threads. I'm fine with that but it does prove that although there is a disclaimer at the top, and people should take it into consideration, in reality if people think someone knows what they are talking about, there is every chance they will act on that advice.
I'm going to drop it now because I am on a bit of a hobby horse!