Difficulties with colleagues

and a grievance will just mean they resent her and talk about about her more and make her life more difficult.

You are in a toxic team and it's wrong and it's vile. However you won't change it so sharpen up your CV and move on. They exist and too often comprise all women teams.

OP doesn't want to be friends with these awful people. She just wants them to be polite and professional, particularly the manager.

This isn't going to get better and your mental health is only going to get worse. Forget a grievance. Look for another job, and then you can think about a constructive dismissal case once you're on the outside.

There are ways of addressing gossip etc and ime ‘challenging’ or calling people out isn’t that effective and just plays into the drama.
If you really feel you have no option but to highlight it, then raise it to your manager or their manager as part of a one to one.
However I’d suggest rising above it as best you can. Do your work, smile pleasantly , have a selection of small talk that if necessary you can use if the conversation is bitching about someone else. Calmly wander off if you think you might get drawn into it. If A asks or comments directly about her so called friends B or C, and it’s unpleasant then again have some useful phrases to hand, ‘oh really, that’s sad to hear, I’ve always found her to be very professional’.
Be bland, calm, professional.
be self aware

it will just get recorded somewhere and ignored, and it will get the backs of the colleagues up, the OP isn't going to magically be invited on the next holiday and swan off into the sunset with them.

Well it might do if it is resolved in favour of OP who is clearly being excluded by all her colleagues. Toxic workplace behaviour should be challenged.

I learned a very long time ago that work colleagues are NOT friends. We had a new female on our team during the time that I was having a very bad time at home. I always kept my home life and work separate but the situation was really upsetting me to the point that I actually looked ill. One particular day, the new person noticed and taking me aside she said she could tell something was wrong and I could trust her if she wanted to talk. BIG MISTAKE! I confided in her and found out three days later that she had shared my problems with other employees, one of which was so appalled he rang me and told me what she had done.

All hell broke loose but I was labelled the 'bad person' because I spoke out about her breach in confidence and made her cry! I wanted to fg kill her to be honest! I never trusted anyone again after that.

Start looking for a new job - these people aren't your friends and those that do associate together outside work only do so as they have a fear of missing out and think that others will be talking about them.

Don't be ridiculous. Although the behaviour in this situation is clearly not ok, it is not 'sad' to develop good friendships at work, as indeed the op has in a past job. We often make friends initially based on some shared circumstances whether that's school, work, a hobby or having children of the same age. Some of my best friends I met at work. Yes we do sometimes holiday together and no that is not sad.

A mediator was involved and OP's colleague was given a warning by HR so the colleague's behaviour obviously violated the company's code of conduct.

Why is it you say you can't get another job? I wouldn't stay in a place like that personally.

Spend far too many hours of our lives working to be in a workplace that's not nice.

This. Go to work, do your job and go home again.

Look for another job. in the meantime buy some ear defenders to wear or listen to classical music and pretend they’re not there.

Some on here saying it's none of your business @Ereerenownow when you see this happening and calling it out; honestly we should all aspire to be better and call out nastiness, not keep our heads down and just be bystanders.

Bullying is never OK, no matter who is doing it or how old you are. Bullying affects people so deeply it leaves them traumatised and in some cases suicidal.

They sound deadful! I am so pleased I am no longer working.(late 50s) Workplace bullying is the worst.I really would look elsewhere ,Bosses are supposed to be calm and impartial they sound horrendous.Sounds like they are very similar.

Pack mentality, some people never grow up it really is pathetic and it's women like this who give us all a bad name.

Agree how sad to have to go on holiday with a bunch of work colleagues. Be glad you're not like them and try to get out ASAP. Sorry you're going through this OP.

I just did some training at work online and they encouraged staff to call out behaviour like OP described.

OOH it's better just to keep your head down, I have a colleague who is difficult and unkind.

Sorry you are going through this OP

I would be looking to leave asap and then on my last day I would be laughing while giving them a few home truths about all the bitching they do behind each others backs.

You don’t deserve this treatment in the work place.

However, you have overstepped.

They are established colleagues and friends.

Therefore, they know what each other is like and although it’s not ok to be unkind about colleagues, it’s outside of remit to try and manage this.

Just adding to say, the last time I went through this, I also had a male boss who sort of vaguely oversaw my direct line manager and all of our work, and HE knew I was a good worker, so my manager's influence wasn't unlimited.

I've worked in environments like this. You have to keep your head down and focus on doing a brilliant job, in your work. It is shite, I admit, but we all have to cope in work situations at times where there is bullying (I'm not saying it's right, BUT if the manager is on their side, you're limited in what you can do).

Good work will always eventually over ride being in the in crowd. BUT it's a nightmare living through it.

Unless there is more to it than we read here, I have to say they sound very cliquey and unprofessional.

I would not stay in that working environment and suggest you look for another job.

@Ereerenownow

"Well she was slagging this lady off to me..not sure what else I should have done."

For what it's worth, I think you did the right thing – although a very brave thing given how much grief these others are giving you.

I'm also the type of person who just cannot stand by and see injustice done / good people bad mouthed and will stand up for what I think is right, even if it means ending up the odd one out.

So I just want to say well done for what you did And good luck for the future. I hope this newer nice male boss takes over and the dynamic may change completely if this other woman retires. It does sound a really difficult environment at the moment. If you think there's a very real prospective that within a timeframe you can manage, it will change, might be worth sticking it out.

Also, would it be worth going to talk to that potential new male boss now and explain the problems in confidence and see what he can do behind the scenes? But you probably don't want to raise your head above the parapet any more than you have already so ask him for a confidential meeting