A FREE MAN?

I have resigned. In high dudgeon.
Yesterday's meeting was a far worse travesty than I was capable of imagining, full of "the procedure doesn't allow..." and "if it was within the timescale..." and "you're fucking joking!" and "this is outfuckingrageous". I did try to curtail my outbursts, but it was an uphill task, and this Bozo was paid to come all the way from Newcastle to tell me what he'd already decided, which could have easily been done by email.
When I came out of the meeting, I had a small and restrained rant at John, my direct manager, about which I felt terrible, as he is such a nice bloke, but he needed to hear it.
So, free from the restraints of being a Civil Servant (God how I loathe and despise that job title) I can now state quite loudly and not-so-proudly that the Department of Work and Pensions supports and condones Harassment and Bullying in the workplace. It doesn't just turn a blind eye, it is fully aware of what is going on and is happy to do absolutely fuck all about it. Let's face it, the whole Department is nothing but one big corporate bully, so why should it differ in attitude towards its staff? I despise the entire system and every bastard who administers it.
PCS Union is equally guilty. Racism, discrimination, bigotry, bullying and harassment are rife in its ranks, all the way to the top. I was summoned to Leeds for my allegations to be heard - how could I expect a fair hearing when I was interviewed by a very loud, obnoxious and obvious bully? (I'm referring here to Jane Aitchison. I think names should be named.)
I have just been phoned by my line manager, to ask whether my email, which said "I have no option but to tender my resignation" should be taken as notice of resignation, or would I be putting it in a letter.
I think a letter would be appropriate, under the circumstances.