Before CV if a. teacher was off they would have to contact their hoy/hod with a lesson plan and a link to any resources as soon as it became clear they were ill.
I'm ex cover staff. 
If there was no work given, as pp. said, we were there to babysit. Students used to love cover days.
Teachers who didn't supply work on a regular basis didn't have their contracts renewed.
Ideally teachers are supposed to have lesson plans and resources ready and accessible to anyone incase they are absent for that next lesson.
Although yes they were supposed to be up and running, some are still having issues due to internal systems/funding/staffing.
My ds school didn't manage to get enough funding to start works until around half term, by which time a lot of staff are off sick and well passed their first lesson.
Now the school are doing their best uploading content, plus all the usual day to day stuff they are doing for their own subjects never mind others.
Plus catch up for the course work missed, hence many students will be in the same predicament of not knowing the exam questions because as yet that material has not been studied. Not all schools were able. to open in June for the years 10. and 12 (?) so they didn't have that catch up. Plus closures since September and the provisions schools were able to get out, also means some won't know parts of the exam questions, and normally they would know it all or a majority of it.