They shouldn't be going out for food if they are in quarantine.You’re allowed to leave the house for:
Essential work -They don’t do that.
Daily exercise - They certainly don’t do that.
Essential food and medicine, with it being specified to shop for food as infrequently as possible.
They were direct instructions, given by the Prime Minister (whether or not you think he’s a cretin or not.) This is pretty clear, so let’s see how they manage with this. 43 trips to Morrisons in 3 days is not essential. Given how intelligent and clued-up they are, they’ll follow this advice to the letter and show just how responsible they are and that they can actually plan a weekly shop for food. It can’t be as tricky as brain surgery.