This is massively confusing - it reads as though if one parent is a key worker then they send their kids to school regardless of what the other one does. There will be parents who take the piss by sitting at home and sending their kids in to school at this rate.
Obviously it means that if one parent is at home then they can care for the children but Boris is expecting parents to not be selfish about this and exercise some caution. - the behaviour of the general public around social distancing and the panic buying is indicative of this fact.
I'm so worried, it looks like (as a teacher) I'll still be expected to go to school every day, work throughout my holidays as a babysitter whilst my child go to their school to have a teacher there doing the same. I'm also expected to continue with providing work for my students and giving feedback.
Maybe it would work better if teacher parents were expected to stay at home with their own child to reduce the number of children actually in school. I feel as if I have to compromise the safety of my own children to babysit other children who could easily stay at home. I know the guidelines say that all should stay at home where possible but people just won't observe that, especially lazy parents.