So as everyone has said....a department closing is a confidential matter.

Thank you for all your information. I will act as I have done throughout. Turn up to all meetings I'm asked to attend and at the end of the day I will be leaving regardless. I just wanted to clarify confidential information when it doesn't say confidential and you have been told your stakeholders are aware. I don't think they ever were aware and thats the issue.

My personal take on it is that you had reason to believe it wasn't confidential, as you were told they were aware of the plan. Equally, you were asked to review something which was inaccurate, and so it was important it was corrected.

However! Whilst I don't agree that 'of course' strategic plans are confidential (every organisation I have ever worked with has published them, and strategic plans are usually well known to competitors as well), I do think there needs to be an element of common sense in which elements of it you share, and when. A department being made redundant *could* be sensitive if it has implications for partner organisations, workload, governance, relationships, brand perception etc. Therefore it's the sort of thing that - whilst the plan may not be completely confidential - I'd have checked it was okay to share, before sharing outside the organisation. Equally, financial information would be in that category - I wouldn't share it outside the organisation until I was certain that was okay to do it, as that could have significant ramifications for a business.

However, I don't think they could argue breach of confidentiality - you were told it had been shared, it turns out there were two plans, and you were asked to check a document which was incorrect so you corrected it. I think they could argue breach of common sense, though. Personally, I'd just be apologetic, explain the situation, and leave it there. You'll be leaving anyway!

Just because it didn't say "confidential"/"top secret" (or whatever) on the front, it shows a pretty spectacular lapse of judgement to do what you did.

Furthermore, whilst everyone makes mistakes from time to time, this could be the sort of "mistake" which questions basic competence - especially from a 15+ year employee. Ignorance is no defence.

Oh my god.

If I were your boss you'd already be out of the building. I'm beyond amazed that you can't see how serious this is.

You're coming at this from the angle:

Everything we are told or sent as part of our jobs is OK to discuss outside the company unless marked as confidential

Everyone else on this thread is thinking:

Everything we are told or sent as part of our jobs is confidential unless marked as able to be disclosed outside the company

Which position seems more reasonable to you?

That seems a bit of a misrepresentation of the OP's position, which sounds more like

"I was told our partner company were aware of the plan so I corrected what i saw as an error in their report."

My guess is they were going to share the information when the time was right for your company. Now you have let the horse out the door to early an they could be on the end of financial and reputational loss.

You've effectively shown your companies hand before the cards were dealt and their partners could now be reacting by cancelling orders/not paying invoices/restricting services under the assumption your company make be going under if it's under difficulty.

You say you've worked there 15 years? My second guess would be they are trying to say bye bye to your redundancy money by dismissing you for gross misconduct.

The misconduct was never taken up by my company and they still decided to offer me another role despite my redundancy.

And have you learnt anything about the wisdom of forwarding internal documents to 3rd parties?