I have posted before about this, but I go to a warehouse type place for clothing. I am not in the UK and I suspect that bales of clothing are bought from the manufacturers where is is sold really very reasonably.
Every few years or so I change my winter wardrobe (sell the used items and use those funds for reasonably priced new items from here).
I was there last week as the winter stock is coming in now, so I was having a good look around, as you do have to have time as some of the items are rejects, so will have nicks etc.
I was looking through the rack of jerseys, there are a fair amount of the same and some have different labels. Some were New Look, some Only (I don't know that brand so if someone could tell me what UK shop this brand is sold in) and then also Vera Moda. Then the others that were the same were Primark and C&A. So these must all be made in the same factory and just labelled accordingly for the shops order. I bought the Vera Moda as although they were pretty much the same, they did just feel a bit nicer and included the string on the back nape to hold the shape (I know this has a name but right now its the nape thingie).
I posted before as I found Clarks shoes in there, and the very same ones with a Cos branding.
Anyway, my long winded post is to say that even though you may go into a different store, it is very possible the items in there are very similar (if not exactly the same) as in other stores. Maybe perhaps some slight adjustments in the manufacture have been made (like the VM versus the others).