Change in job role following maternity

[boatyroo]

I've returned from maternity leave recently. Prior to leaving I managed two employees, my job title was XX Manager, where XX is a specialist area. One of these employees moved teams while I was away and wasn't replaced, the other was still there when I returned.
Towards the end of my maternity leave (I took 1 year), I was emailed (to my work email so didn't see it immediately) by my manager they were recruiting a role 'manager for XX' but my role wouldn't change. I would report to this person.
When I returned I found the job description on our intranet which was very similar to my own (having ownership of same things). I told my manager I was confused but he reassured me again that my role wouldn't change.

Now the new manager has started. She has worked at the company a long time, but has no experience of XX. I basically have no responsibility for anything I did. She has said it would probably make more sense for my direct report (who is very annoyed about the whole thing) to report to her instead, but is still deciding. My report and I would then both have some responsibility for some areas. I have said that would feel like a massive change to my role to me. I have said it feels like a demotion and they said that isn't the intention. I don't think my new manager is even aware of my job description but I feel a bit confrontational showing her.

I don't know what I should do - is this allowed? Is it worth speaking to HR? Some people have told me it sounds like constructive dismissal but I am not sure if it is or if it is ok, just very frustrating for me. I have 10 years experience in the specialist area.
If relevant, I had a flexible work request agreed for slightly reduced hours.
Sorry if I've left out any details. I would really appreciate thoughts on this.

Just to update on this, i emailed my previous manager to say I would consider it a significant change to my role if my direct report were to report into my new manager instead, and that I had been assured twice (luckily once in writing) that my role and responsibility would be essentially unchanged.
He has said they disagree as I wasn't recruited as a people manager and they didn't see it as a key part of my job, and I should view it as a development for my direct report rather than a demotion for me.
I also have in writing from when I first got the position that they were recruiting someone to report in to me.
Previous holders of my position have all had management responsibilities, and a sister company has someone in the same role who manages someone.

Should I now contact HR to get their view?
I don't understand how they could say that removal of management responsibilities and loss of any authority in my area isn't a demotion?

Please call ACAS and take proper advice on this before proceeding x

Thanks, I will do.

@boatyroo, Can you report back once you have spoken to ACAS? I am in a very similar situation. Very curious to know what advice you receive.

You need to decide in real terms how much your responsibilities have been eroded in your "new" role, i.e. how different the job is now (duties, skills, people management) compared to your pre-Mat Leave job.

Gather your facts then book a meeting with HR, where you express concern, show them specifics of how different your job is since you returned from maternity (that's the important point). The company position may be one of denial "your role hasn't changed, you are still the same seniority" etc. If you can put forth a strong enough argument that so much has changed (including loss of direct reports, role duties overlapping significantly with other staff etc), they will take you seriously, as they may see the starting of a Tribunal case on heir hands (without you saying as much!). Keep it factual and succinct, non-emotional.

The next step, if they continue to deny everything, is to put it in writing as a Grievance, which then forces them to take you seriously, as they will have to investigate your situation formally.

You could include a remedial suggestion in your Grievance, which is for your employers to find you another role of equivalent seniority to what you enjoyed before your Mat Leave.

What they've done isn't necessarily "wrong" - they could argue you were away for a year and the needs of the business have changed. What they must do, however, is respect your equal rights in maintaining the position you had before (either actually, or as an equivalent role elsewhere in the company). Your maternity leave should not prejudice your ability to maintain your position and standing in your company (which it appears to have, based on your description).

Thanks a lot for the detailed response daisychain01. Still considering my options at the moment!