Informal meeting that was actually an informal meeting

[Garethcheese]

Hi,

I have been in my current job around 2 years and 7 months. Recently i was invited into a so called chat. I thought that this was an informal meeting but actually i was joined by a UK Director, EMEA Director and HR via Teams.
I was told about the meeting 3 hours before, by calendar invite, which just said catch up and had no agenda.
I was the told that my performance was unsatisfactory by them even though being a Sales job i am hitting my target and given no clue to what other KPI's i was being assessed on.
They told me would instigate a PIP after 10 days but actually arrived after about 14 days. This did give me some targets and why institigated but they were not discussed during my meeting and given any basis.
I have looked at the disciplinary procedure and all it effectively says is an informal meeting would be a chat and potential councilling but i understand in those cannot instigate a PIP and have multiple people present.
I also had no time to obviously prepare to defend myself fully.
I have spoken to ACAS and advised my company i will not adhere to the PIP and outlined that I have not been given the adequate training to perform the tasks in it and also why a strategy they suggested had failed. This is all in writing and i have copies.
I just wanted to check that the above is not legal and i also have several other items i can bring up with them regarding holding back holidays after a grievance and some whistle blowing actions.
I am obviously looking for other employment but if they can back and try to put me on a formal disciplinary can they do this and do you think it would be worth putting in a grievance immediately to cover the above issues?

[Garethcheese]

Apologies the heading should be an informal meeting that was actually a formal meeting

[ULA]

Informal chats with employees can be precursors to a number of further actions including changes to roles, responsibilities, performance issues or disciplinary action.

If the company does not believe someone is performing then a PIP is a recognised way of managing and trying to gain improvements in that person's performance. It would only be once this process has been exhausted without any improvement that disciplinary action could be instigated.

Part of the process of a PIP is that there is a documents which sets out the performance improvment requirements, usually with objective, timescales and dates set for regular review and feedback on progress. It is normal that a PIP will cover a period of several months to give adequate time for the improvements to be made. If part of this, in your particular situation, is that you feel you have not had adequate training then you need to highlight this as part of your PIP review, ensure that it is documented and get an agreement as to what will be put in place to get you the requried training.

What has happened since your meeting and you being provided with the PIP?