Just to add to this, make sure you register on government website that you are vulnerable: COVID-19: guidance for people whose immune system means they are at higher risk - GOV.UK - when I first did this for my dad we were relying on friends and neighbours for shopping and there was a question on the form that asked if you had this help, so I put yes. We registered with supermarkets but couldn’t get any slots. Someone at Dr surgery then told me to re-do the form and put that we didn’t have help so I did that and this then got passed to supermarkets who gave dad priority slots. That said, I’ve had to sign on with 3 supermarkets and spend an inordinate amount of time checking for slots almost daily to make sure he can get a weekly shop delivered. You might also have local wholesale businesses who will deliver to private households now as their restaurant business has dropped off. We have a great local one that does fruit, veg, dairy and quite a bit of tinned food. Bit pricier on some things but they’ve been a big help.
I have paid extra with Tesco to get advance booking of slots. I book in advance.
Every day new slots are released, so I always book on the day just released. You can book a slot, say that you just want a packet of biscuits, and then checkout.
Nearer the date, you can go back to the order and buy whatever you need at the time.
I didn’t realise until recently that although you checkout and give your card details, they don’t take anything for an order until they’ve made it up for you, so 24 hours before delivery.
I also do “click and collect”, which in some ways is better for me than a home delivery.
If you do this, take some plastic boxes in the boot of your car and then ask the staff to load them up for you.
Next time, I’m taking some larger boxes, the same size as the boxes they pack in. Then they can just lift the box liner, and put it all in my box in one go.
In either case, the best time for me is often 2-3pm, this time of year. It’s still daylight, and lots of parents are thinking about school pickup times.
Hope this helps.