Before even writing this, I upvoted @Gregory's answer, as I think it's succinct and addresses OP's issue. However....
OP, make a free appointment with Citizens Advice Bureau. They will instruct you on what to do next. Do this soonest.
If you use a computer (assuming you are an office or IT worker), make sure there is nothing personal on it that you might need later. Copies of CV? Personal Banking? Bills? All your favourite Dilbert/other cartoons or jokes? Browser favourites? Music collection? iTunes / Other? - deregister that machine now, while you have a chance.
We've all been told to do nothing on it but work stuff, but, hey? We're all human and we all do it from time to time. If you're terminated with prejudice, you will be leaving the office with nothing but your coat and bag and if you're lucky a kindly colleague might put any personal stuff from your desk into a box for you to collect later.
As stated in comments, make sure you forward and print any emails. Also get a copy of your employment contract AND copy of anything (employee handbook) which documents grievance and termination process. From this point forward, the best outcome would be you finding another job quickly and putting this behind you. Make sure you either get counselling or a least talk all this over with someone, else anger and bitterness will stay with you for a long time.
Read and reread the grievance procedure. If you are threatened with termination, counter with "So the next step is formal warning / Personal Improvement Plan....?" whatever it says. If they really want to get rid of you, they'll follow their own procedure to the letter, as not doing so will leave them open to a claim for unfair dismissal. (Not "constructive dismissal" - that's different).
If you do go down the legal route, seeking compensation, the most you're likely to get is pay in lieu of notice, and maybe another month or so on top - it won't be tens of thousands. Make sure you include your legal costs in any settlement.
As stated in another comment do not threaten to sue the MD. Your case is against your employer (the company). In fact don't make any threats. Just smile back, and get everything recorded (either literally, or on paper). While we're on the subject, if you have any kind of disciplinary hearing, make sure they give you at minimum a few days notice, as you're entitled to bring a representative with you. I would also suggest getting a small dictaphone for recording any meetings. Do so honestly and openly; it's to allow you to take accurate "minutes".
Do not sign any piece of paper without first taking advice. Don't fall for the "you have to sign this, or we can't process your last payment" lie.