CSCC has just published its draft calendar for 2020. No details yet of which series runs on which day:
28/29 March Snetterton (300)
18/19 April Cadwell Park
8/9 May Brands Hatch (Indy)
23/25 May Oulton Park (International)
26 – 28 June Spa Francorchamps
25/26 July Thruxton
22/23 August Silverstone (National)
26/27 September Donington Park (National)
16 – 18 October Le Mans (Bugatti)
1 November Mallory Park
I see Andy posted a thread almost simultaneously