AIBU to feel upset after my meeting with my manager?

I agree that you have grounds for constructive dismissal. You have been treated disgracefully and summed it up well by saying your appraisal was a character assignation. Even if you don't want to go down the tribunal route I think you should state this in your resignation letter or email. Your employers sound awful so leave with your head held high and don't look back

Litigation - personally I would not. Everyone I know who did this is still talking about it 10 years later, it's traumatic, like a divorce. Sometimes silence and moving on is more powerful. You can still kick them in the nuts at the exit interview and by letting one colleague know how you feel, the vibe will travel.

OP do you get full sick pay ? Or just SSP?
If the former, be a bit more strategic and exhaust that up first otherwise you’re cutting your nose off to spite your face.

Go for it, if you are leaving anyway you have nothing to lose.

Great idea.
Also spell out the bullying going on, which you have witnessed and reported to X.

How you have been advised externally that your treatment now, may be a direct result of what you have reported, and you are in effect a whistle blower.

Mention your profound disappointment at how you have been treated by management after your years of consistent effort on the company's behalf.

You can also choose to cc the CEO.
There is little as powerful as putting things down on paper, naming people and copying others in.

You completely take away their ability to deny knowledge of illegal behaviour like the bullying that is going on.

I have seen it used extremely effectively in several occasions.

Yes, he needs to know what is happening so that he can do something about it if he wants to. If he doesn't then he deserves what he gets.

Now this is a much better idea than writing a report. As for copying in the CEO, do you know them? Are they an arse as well? I ask only because behaviours such as those you have witnessed often trickle down from the top. If you have any doubts, my suggestion would be to contact the person you DO trust. If he “has the ear of the CEO” he’ll tell them anyway.

National minimum wage for a decade? You have never asked for a pay rise or they have offered? 10 years?!

Apparently they have observed this about me for a while, and my manager should have addressed it with me, but they did not. Even though I spent an hour and a half in my appraisal. Apparently they are too scared of me.

who told you that your manager was too scared to raise this?

I'd have quit on the spot quite frankly, cleared my desk and gone off sick for whatever notice period was required.

Even if you don't want to do the full constructive dismissal thing it's worth mentioning in your resignation email as your employers will probably take legal advice and waste a lot of their money.

I did this and it gave me great satisfaction to find out that the legal bill was massive and much more than redundancy would have cost them. I did get my union to write to them which apparently caused the director to nearly have an apoplexy. Incidentally OP, if it makes you feel any better I was told in an appraisal that I couldn't be considered for some tasks involving contact with the trustees as I was too common and they wouldn't like having to deal with me!

Also this.
Plain resigning, mentioning your reasons, your whistle blowing, your witnessing illegal behaviour, being targeted because you spoke up, will all give them pause and indeed, particularly if you mention you have sought employment advice, will definitely have them wondering whats coming down the line.

Again, peppering it with management names an cc's gives them zero cover and deniability.

This will piss them off so much.

I did it 30 years ago in a toxic environment after walking out of a contract position.
I had HR all over me wanting to fix it, and they admitted the Board of Directors were on to them asking who the hell is this? what has she written about? and copied us all on.

I took great pleasure in rightly shitting on a bullying manager who thought he could treat me poorly and needed the position.

Management do not like their names attached to negativity in my experience.

What was the massive legal bill for?

Bloody hell, this place sounds similar to my old workplace. Badly managed, defensive leadership instead of solution focused, managers inability to truly reflect and build effective strategies, would rather everyone just shut up and be accepting of shite, enjoyed the power.

....sounds like my current workplace ☹️

Haven't RTFT so caveat that other people probably have more relevant knowledge than me. But I got legal advice on constructive dismissal from my last place due to them refusing my flexible working request and disability accommodations and not supporting me with alternatives. I was told that constructive dismissal is very hard to get and you have to show that there has been a breach of contract from your employer and that you resigned in response to that breach with no delay. I had found another job first so it was a couple of months later (but still while the appeal through work's processes was ongoing) and that was one of multiple reasons why I didn't have a case, so it might be similar if you don't resign until you have upped your hours at your other job.

The contract terms that have been breached can be implied so eg the breach the legal advice identified in my case was a breach of the 'implied term of mutual trust and confidence' but I would have had to show that there was 'no reasonable and proper cause for the employer's conduct' and that 'the conduct was likely to destroy or seriously damage the relationship of trust and confidence'.

Not to put you off and obviously get proper advice but you are right to be asking yourself if it's worth it. I found just going through the initial steps very stressful and upsetting and I had some union support. I did it not expecting to gain from it personally, I just wanted to hold them accountable to hopefully stop it from happening to someone else and I absolutely did make my work sweat a bit so hopefully they will be less blasé about not supporting people in future. I don't generally believe in going over people's heads but someone told the CEO why I was leaving in my last week and she met with me to understand what had happened before I went. I think your idea of contacting the senior guy is a good one.

I am so sorry that it has made you feel low and question yourself. You sound like a great colleague who cares about doing the job well and improving things. I'm sure you are right that ageism is a factor but for what's it's worth, I am still treated as a youngster at work and I have had a lot of jobs and my opinions are often not welcome! Yes being competent and unafraid to speak honestly in meetings does not normally make you a lot of friends. But people being afraid to speak up and have ideas to improve things is what holds organisations back. In the right culture it's a huge asset. Don't change who you are just because some other women felt threatened by it. Unfortunately we don't always support each other and instead fight over the scraps our employers might chuck us.

Oh and PS the only other thing I would say is take sick days when you need them, whether that's for your physical or emotional health. Your employer will not be there for you long term if your health fails you and won't appreciate your sacrifice, as you have found out. It's not a badge of honour to work when you're unwell and it models other people not looking after themselves either. Obviously if your employer doesn’t pay proper sick pay that's different though.

When it reaches this level of toxicity, it's imperative that you leave for your own wellbeing. I have been there and it nearly destroyed me.

I left my former employer with a financial settlement because they knew I had enough evidence for an employment tribunal. That's an avenue worth considering for you I think. I didn't have another job to go to, so the money saw me through.

Take the money and develop your pilates business.

I'm now a self employed contractor, valued, respected, asked to stay on repeatedly to do a variety of interesting work that I just wouldn't have done in my previous role. And leadership listen to my advice.

It took a while to rebuild my confidence after everything that happened. The best way of doing that is to do something that you enjoy and you're good at with a level of autonomy.

Good luck op.