I think the confusion came about because in the normal course of events you do not need any kind of sick note for the first 7 days of an illness.
However as the business has said that the majority of Coronavirus related sick absence will not be considered for the attendance procedure members ideally need evidence that their illness/reason for isolation is related from day 1.
Another reason for confusion was that the isolation note was positioned as a replacement for a fit note, it isn't. It only covers the recommended isolation period for either symptoms or living with someone with symptoms.
As far as I'm aware the NHS website has not changed at least since the 21st March which is when I used it.
The video is talking about getting a self isolation note to cover days 8-14. That is what I originally told the OP. Self-cert covers days 1-7.
There are only two reasons why you wouldn't return to work after day 7.
1.You are not improving, this means you are now sick and should contact NHS111 immediately who will give you guidance on what to do next. This is very important because having this virus for more than seven days is a major red flag. An ongoing cough after 7 days is not considered to be a sign that you're still infectious. It may be that if your symptoms are still mild they advise you to continue with isolation but if this is the case ASK FOR CONTACT DETAILS.
2.You were not the first person in your household to get the symptoms in which case you would have received a 14 day isolation note from day 1.
All of the advice I've given is based on following PHE guidelines to the letter and not giving management any wiggle room when it comes to the attendance procedure, I am of course aware that different managers will try to interpret the guidance in different ways and even union reps will be confused and misinformed. Even ACAS have muddled guidance on coronavirus.