Not everyone might have £100 spare. But one month they may have £40. Another, £20 etc. They don't need to buy everything at once. Then, when they have it, have got it to use repeatedly
And yes, as someone who has lived out of London for 30yrs, I can confirm pretty much everyone has a car! Swap "London" for "big towns/cities". I live on the outskirts of a small town. I would not be able to get a pint of milk without a car. I don't know anyone locally who doesn't have a car. Of my friends in London, I only know one that does.
I spent a period of time, with one DC on benefits, and it truly baffles me how people are in this level of poverty. I almost couldn't believe the amount of money I was just being "given".
They pay your rent, council tax, your water bill is capped, you get free fruit/veg/milk vouchers. I honestly couldn't believe it, and lived no differently (day to day) than when I was in employment. I wasn't treating myself to shoes I didn't need perhaps, but we were very comfortable. I truly don't understand, how when I was on the same benefit income, I was more than covered, and yet people on the same, are in such poverty that they can't find £20. With the exception of the initial delay when enrolling for UC (and that's a one off temporary thing) after a couple of months, I don't get how people have "no money". I've been there, I'm not a special case. It was more than enough.