IANAL but given the unreasonableness of the premise as I read it (? scraped data from public websites of multiple companies is "owned" by some mysterious third-party) this sounds more like a consequence of the UK's legal system, where minnows have to shut down when challenged by sharks, because the costs make it impossible to resist, regardless of the strength of the case.
Also, its all a bit vague, especially the reason for the donations - to pay these jokers off? That just enables and encourages the bullying. They should provide more transparency as to who is claiming ownership, and what evidence is being given and legal arguments for paying.
You generally don't own the copyright to images that you scrape from the web, even public websites. A number of companies handle consumer product information internationally (such as GS1 for barcodes) and shops license product information (images, EAN Codes, nutritional information) from them, so they don't have to deal with each manufacturer individually. The manufacturers also work with these organizations.
If they went into supermarkets and took pictures of all the products it would be another story, but as is, they are using pictures on the internet in a way that they aren't licensed to. This is not particular to the UK, just because some site display a picture publically does not mean you are allowed to display the same picture on your site.
The cease and desist letter stated: "proprietary images and data", I doubt a commercial/sponsored database of prices exists. That would have grave anti-cartell consequences. But you're right: for most reasonable people reading the article, the _only_ relevant data on trolley.co.uk _would_ be the price information. (And I don't have any insider knowledge, I was only guessing ...)
Also, its all a bit vague, especially the reason for the donations - to pay these jokers off? That just enables and encourages the bullying. They should provide more transparency as to who is claiming ownership, and what evidence is being given and legal arguments for paying.