So I guess Wal-Mart is to Lidl, as Tesco is to Jimmy's Grocers.
While I generally like Mitchell and Webb, this sketch is outdated without being clever. It's like Seinfeld or Leno saying "What's the deal with cellphones? They're bigger than you're head!"
The irony is that a lot of store-brand cereals really are better than the brand names. "A pound of puffed rice sprayed with chemicals for only £5. You'll buy it because your kids won't shut the fuck up unless you do, bitch. (Plus free piece of crap.)"
and Big Lots, where a box of cereal that normally sells for is somehow magically just .50. And their entire marketing campaign is centered around trying to convince us that really there isn't anything wrong with it.