See actually, this is a bit of a game changer. Over £500 on groceries but no alcohol? What are you buying
It's easily done though, especially in Waitrose. It's about £15 or so a day, or £7.50 each.
You can spend over a tenner on a nice sushi box that's a light lunch for two.
A curry meal deal is another £10.
Charlie Bingham's ready meals are at least £4 a portion.
All the fancy fruit pots etc.
You get the idea. There is no normal amount.
There's an amount that's needed to adequately feed an adult and the £40 a week seems in the right ball park. Of course, some people won't even be able to afford this and it can be done for less and still be healthy and sustaining, especially if you can cook a good range of cheap meals with seasonal veg, pulses, spices etc, which can be very cheap if you buy the larger packets of Asian brands etc rather than the nice Bart's tins in Waitrose.
Or you can spend far far more. And as for the 'eating out twice a week' comment, some people eat out far more than that, especially in normal times. They might almost never eat at home. Coffee shop breakfast during the commute, lunch from the myriad of options if you have a city centre job, couple of restaurant meals out a week, maybe a takeaway and a Gousto box for the rest of your evening meals and even if you go to cheaper places like Greggs, McDonalds, supermarket meal deals and the like, rather than Pret, Wasabi, Nero etc you're probably averaging close to a fiver a meal to feed just one person, so that's £450 a month just there, probably more.
I have no idea what we spend. We get a takeaway about once a week, DP buys either his breakfast or lunch at work most days, but pays for some of that out of his personal spending money, rather than grocery budget, I try to get a takeaway lunch about once a week while WFH.
But then I do cook proper meals as well so it balances out, especially as I make a lot of Indian vegetarian meals that are literally pennies a portion.