Supermarkets will use a government database of 1.5 million vulnerable shoppers to help prioritise delivery slots during the coronavirus pandemic.
Sainsbury’s and Waitrose say they will begin writing to people on the list next week.
There is concern those most in danger from the virus are going in to stores due to a lack of online shopping slots.
People in high-risk households have told the BBC they are struggling to get priority treatment online or in stores.
Sharon Cranfield from Tadworth in Surrey says her 19-year-old daughter Jessica is very vulnerable to coronavirus because she has cystic fibrosis, which means she needs an “athlete-style” diet of 3,000 to 4,000 calories a day to survive.