For anyone it might concern.
Sainsbury e-mailed me to let me know they will be releasing daily delivery slots to customers over 70 or in the at risk category. It started yesterday and they seem to be adding dates a couple of days ahead so I've been able to order a delivery for this Thursday. Understandably they are restricting it to one delivery per week, but at least it means we will be able to have fresh veggies etc each week.