3.5 months later, I may have been hard on the Wilko products but it's there is still suspicion because the pockets (in the photo) seemed to cause the cat to have more serious bleeding in the mouth at a later date, and then she became almost incapacitated after losing weight quickly. The vet said she suspected cancer, but she said that tests would be expensive and she recommended putting her down the next day, She even booked an appointment for it, which I had to call and cancel if I wanted to.
Cat then steadily recovered to her old self (seemed to be helped a lot by me bringing water to her in a bowl. She'd always ignored the bowl before because she preferred water from a tap.) Three weeks went by and she got her weight back, obviously enjoyed drinking from her bowl now, and was recently ripping around the flat when in good spirits.
After four weeks with nothing but improvement in cat's health, some more bleeding from the mouth occurred, four days ago after eating a small amount of the Wilko cheese flavoured creamy pockets. The bleeding didn't last this time and her condition didn't dive-bomb like before (see the p.s. below.)
She was right as rain last night, sat in the window watching a cat outside which comes around to look at her, and was up to her normal activities early this morning (e.g. up on the table and into the window.)
She is normally choosy over what treats she wants from day to day, and today she kept begging without eating anything offered. I had mentally 'banned' the Wilko cheese-flavoured treats after the last mouth-bleed, but eventually I gave in and let her have some. She ate them very quickly and. within an hour or two (I'd fallen asleep), was crying out loudly and became violently ill. She has been immobilized on the floor for a few hours, just now sitting up at least. She vomited back the contents of her stomach after I got her out of the cupboard where she'd collapsed. She'd staggered to the kitchen to find a quiet corner. The vomit is very reddened and smelling, in part, like half-digested treats.
Obviously, I have considered the vet's opinion seriously but she did a very straightforward inspection and looked at the scar on cat's tongue from her PDSA operation ten years ago, for an abscess. She didn't really justify her suspicion of cancer with any technical details, but I expected she's seen cats with cancer before.
It's still odd that I'd become wary, in particular, of the Wilko cheese-flavoured pockets, and that there's no doubt at all this time that they triggered this sudden calamity, which has been the worst the poor cat has suffered.
p.s. There was one other product in July which I suspected was involved in the first very serious illness which began two days after the first serious bleeding in the mouth.
The mouth bleeding fitted descriptions of stomatitis on the internet. Sadly, vets don't have a lot they can do for stomatitis. Then, my Google searches led me to a product being sold by lots of eBay vendors, and by a couple on Amazon. They are all selling the same, 'natural antibiotic' in a small bottle. It claims to boost the cat's immune system and, if you search for it, there's an ebay page dedicated to claiming that it is the answer for stomatitis. Cat ate one dose (a couple of ml) after her first big mouth-bleed in July, added to some soft food, and then her condition dive-bombed, and that's when she was taken to the vet the next day. That medicice wasn't cheap (£17), and only when it arrived did I see the label on it: "made in China". I wouldn't recommend the stuff to anybody.
However, I have not yet been able to separate the eating of Wilko treats from the occurrences of mouth-bleeds. Today's sudden calamity occurred immediately after she'd eaten the Wilko cheese-flavoured pockets eagerly. It seemed she'd died at one point and it's still very serious.