I've been Sam Vines broke before. The trouble with saving a little bit every month (let's say £5) for the £50 shoes is that it takes 10 months to save £50. And that assumes no other one-off expenses (a larger than expected bill, an essential repair, an emergency transport cost) set you back during that period.
If your shoes have holes in them and the soles are flapping and letting in rain (which I've had happen to me many times) ... then you need new shoes NOW. Not in 10 months.
Getting a good pair at the charity shop, or off eBay or Vinted or FB relies on a lot of luck.
When you need those new shoes, there MAY be a pair of shoes at the charity shop that are in your size, not too manky, and feel ok on your feet. Or there may not be.
When your shoes finally break, there MAY be a good quality secondhand pair of shoes online that aren't half-destroyed, for sale at around £15 (so... three months of saving, instead of 10). Or there may not be. The seller MAY be honest about the condition of the shoes ("very good condition, only worn a few times ☺️"), or they may be hiding flaws from the photos and unwilling to accept a return or pay for your return postage, should you be dissatisfied.
That's why Sam Vines shops at Primark.
As for the more fortunate population who could afford the £100 ... I read once that one reason well-off people maintain that status is because they won't max out their income on things like food, clothes, mobile phones contracts, utility bills, mortgage interest rates, etc. The more well-off put in the time (since they have that luxury) of seeking out the lowest acceptable price point for the thing they're spending money on. Which leaves them more income for things worth saving for.
Community Clothing, which will be supplying clothes to Team England for the Commonwealth Games, makes nice-enough quality clothes in England. It's about as locally made as it gets. If you shop there, you will be spending between £60-70 for one pair of trousers, £39 for one long sleeved t-shirt, and £4 for one pair of socks. I bought a 4-pack of their socks for my DH last Christmas as a present, and with regular wear and washing the elastic at the cuffs is already starting to go.