Angry my manager has taken away WFH perk?

Agree with this. Same as when OP said she's expected to get co out of the 'predicament' that the person covering her role got them into. Well, if that's your job, then that's what you do in your working hours. It's not doing them a favour.

if they made the offer during your last ML in writing, and it was open ended, point that out.

Look for new jobs, and/or look for different positions within your company.

Breakfast clubs aren't the end of the world. Hundreds and thousands of us have had to manage, and you will too. Having said that, your DH also needs to come up with some solutions too, it shouldn't all be on you - yes, he did the last 3 years. That is not an extra lovely add-on. It is being a father.

But. Your position sounds strong. Why not make a counter offer? poinit out all the facts of your last years work, that WFH was in place of a pay rise etc. And next time get it all in writing and added to your contract.

So, have you been WFH for 6 years or two years? I'm confused

Sure, this is a valid option…
if you want to be an arse to a company you’ve worked for for 15 years and has been supportive and flexible over that whole time, but is now putting its needs in the mix when considering another flexible working request.

Then the application will be rejected. My point is that there's a process for this, and at present it's not formalised.

The point remains. It's an unofficial arrangement currently, and needs to be formalised one way or the other. The op has no 'right to anything at present.

Stop being accommodating.
Stop helping them out.
Start looking for another job.

Get your contract out and start working to it only.
Be a lot less obliging.
Keep note of every time you are being imposed upon.

Just checked back re. longstanding arrangement - the OP started off saying this 'perk' had been in place for 6 years, but in a later post she says:

i used to do
7:45 - 3:30 Tuesday to Thursday
2 years ago, I asked for a pay rise, it got denied but he said he will increase my hours, I said okay but only if I can do it from home.

So the Friday wfh isn't a 6 year-long arrangement, it's only been since 2 years ago, a chunk of which is mat leave. Not saying this invalidates her wish to keep it, but it's not quite the longstanding arrangement some have taken it to be and the deal made with the manager when OP considered the other job 6 years ago has since been modified with this wfh negotiation. So it's really not about a 6 year long set-up. Things have changed in that time off the back of OP's requests and are changing again now off the back of her requests. Wanting her in the office for already short days Tues-Thurs seems reasonable, and cutting the wfh hours (which OP already proposed halving) makes more sense for the business than whittling one of the office days down to a 2.30 finish.

No, the perk would still be there if you hadn't requested the change to your working hours. You have asked to do fewer hours. Your employer has accommodated that request in a way that best meets business needs. They have retained what they see as your most valuable hours, and reduced the ones they can most easily manage without. It would be very difficult to show this was unreasonable in the legal sense of the word. Had you not requested a change and had returned to be told your WFH had stopped, you may have been on stronger grounds.
Your managers informal promise of flexibility is meaningless unless it was written into your contract. However, as they clearly valued you enough at one time to use it as a carrot to retain you, you could try negotiating with them, telling them you will be looking to move on because of this change.

I'm struggling to understand what sort of childcare you must have with one child at nursery at one child at school, based on the hours you originally wanted.

However, can I suggest your easiest childcare pattern would be to work a longer day on Thursday (or whatever day it was you were proposing finishing at 4.30) and beefing up the childcare on that day, so that you can split the remaining hours between the other two mid week days within school hours, to enable easy drops off and pick-ups and have Friday off altogether.
I do wonder if the reason for refusing your Friday wfh is because it's such a short time (variously described as 2 and 2.5 hours in this post).

Because that is the reason stated by the manager.

You requested less hours. He's agreed but not in the way you wanted. Nobody else has your perk. You probably need to change jobs.

I think the difference is OP wanting to reduce her hours onsite without it affecting WFH. If the manager can show that this will cause operational problems then he’s within his rights to refuse the request and offer the alternative best suiting the business - which is that the 22 hours OP now wants to work is entirely office based. OP is now saying that will include 2 hours in the office on Friday mornings. That’s reasonable too because the overall hours she’s actually in the office are reduced.

Based on what OP has said, if the manager has brought in cover for OP’s maternity leave, that person wouldn’t have been working from home - only OP was allowed that as a personal arrangement. So the manager has likely had the opportunity to monitor whether a different working pattern has been advantageous. If that’s the case, it’s OP who has opened the door to the changes by requesting reduced hours. If she’s working less hours overall, then l think it’s unreasonable to expect that the reduction in hours be applied entirely to WFH, as it would reduce the time spent onsite when she’s needed.

This is what I was going to say. If it’s an established norm for such a longer period of time, you don’t need to ask permission to do it each week so it is accepted practice by both parties, it can become an implied contractual term even if not written into the contract and they could not, in that case, unilaterally change it. Seeks advice from a specialist employment lawyer.

Make a formal flexible working request (don’t call it a perk, it’s flexible working) and in that you can describe how the role can be done the way you’ve been doing it prior to your mat leave

How do you know that from the OP's posts without knowing where she works or what she does?

I think the OP should appeal - the business needs to explain to her the reasons and what the business concerns are. Maybe it is what you guess, maybe not. Maybe there is an arrangement they can agree on that works for everyone?

It’s not the maternity that’s meaning the WFH is being taken away is it? It’s the fact you’ve made a flexible working request. He says he can’t accommodate what you asked for and has proposed an alternative. If you don’t want that, you can return to work on the same terms and conditions as when you left - which included the WFH on the Friday morning.

I can understand being upset at not getting it but why would you be upset someone else did?

But you don’t know it would still have there. There’s a huge move towards getting people back into the office.

This. Then if it’s a no and you’re confident they need you, I’d say thank you I am unable to work in the office on Fridays so I will need to request 2.5 hours less a week.

The difference is that OP wants to work less hours. The business can't accommodate making Tuesday to Thursday shorter days so want to remove the Friday.

You didn’t say that in your OP.