OP I've been wondering this since around January when I noticed packs of apples were in 4s not 6s fruit. Pretty certain price of these has gradually crept up but I can't be bothered to verify.
Your post isn't about coffee or co-op as such but it gives a very good example.
The only instant coffee I like comes in 190g jars so standard sizes. It used to be £4 beginning of the year as far ad I remember. Often on offer, all instant coffee seems to be, so I was buying 2 jars on offer. Then the price grew snd grew, less regular offers, and now it's at £7. I can sometimes find in at £6/jar which still seems expensive to me. But that illustrates the scale of the problem.
I tried a lot of alternatives and don't like them one bit. While I can buy this one, I will continue to do so suspecting that the producer and supermarkets maintained their margin. In a perverse way I am encouraging them because they can see this product continues to sell at new prices.
If the time comes when I can't afford it , I will use a less palatable alternative that I can afford. I know I won't give up instant coffee.
Faffing about with my coffee pods or the cafetière is annoying during the day so, although I do like the taste of that coffee more, I barely use it.
What's this nonsense from some PPs about coffee is not essential, don't buy it if the shop is too expensive for you etc etc?
Butter is not essential either. It really isn't. But a lot of people use it, like it and it's a staple of their consumption.
It's exhausting comparing prices and by the time you plan a shop around best offers and do all the travelling, what you might save on particular items is lost transport or time. People forget that time really is money. Realistically, a lot would earn a lot more money during this 'planning time' than they'd save by taking advantage of offers.
Trolley.co.uk is going by the way. Found it recently and it is a useful tool.