Update for those interested.
Stuck my notice in today. Not a peep from the CEO since I sent it first thing this morning. Couldn’t do it in person because CEO is travelling. Fine. The email was very professional in tone but I deliberately did not offer any specific reasons - because I knew they would follow up to ask me and I want to be careful what I put on record.
As predicted got a call this afternoon. Not from him but from his lacky. Very polite conversation, he asked me “Sorry to hear this. Why? Do you have a new role?”.
I did say I don’t have another role because I don’t want them getting litigious thinking I’m going to a competitor which a colleague recently did - they have a lot of resources to make life difficult. I gave him one of the major and uncontroversial reasons for leaving but told him “there are more reasons that I’m happy to pick up in the new year through the proper process” (He was definitely recording it to forward on, he does this often)
One thing I didn’t mention in my OP - I have already booked out this week and the office is closed after Christmas for some reason. So I can effectively do nothing until Jan. That gives me time to think and plan next steps.
I’ve decided I am not taking a sick note, partly out of principle but also because our sick pay allowance is significantly worse than just logging on and doing the minimum for 3 months. Let them put me on gardening leave if they have to.