Not in my experience.
For instance if you compare McVities Chocolate Biscuits with the Lidl one in cheaper packaging, you’ll probably notice that the Lidl one has a different fat content — which is why it tastes cheaper. Lidl have their own brands.
And I just noticed you misread my post Lily so I honestly can’t bother answering you in detail. I realise that sometimes you like being an argumentative toss for the sake of it but if you were to go back and read what I wrote you might find the trick you missed before you contradict me next time you silly boy.
Giving money saving tips is being argumentative?

. I will rise above it.
While your example is probably true, the ranges of own brand biccies says they have a supplier, probably Fox I think looking at the range.
One off items are different, 2 of the top of my head I buy regularly, one may resonate with you.
Tunnocks caramel wafers, the Lidl own brand is exactly the same, while I have not read the small print, I have bought both, there is no difference.
Most cereal is own brand, but they sell Weetabix only in 36 size pack, next to their own but less than half the price, the quality and taste is exactly the same, they are in the same white packaging, 3x12, inside a different box. I have not done a scientific test on them

, but having bought and consumed Weetabix for many years, I cannot tell the difference.
My friend says she has been buying Lidl cornflakes for years, for her mum who will only entertain Kelloggs, puts them in a Tupperwear container and she has not noticed, know idea who supplies those, but good enough anyway.