Damn. I never knew that. In fact, I had to Google it, and this is what I found:
Traditional British chip shops primarily use non-brewed condiment, a mix of water, acetic acid, colorings, and flavorings. While many call it "vinegar," this cost-effective, non-brewed alternative is used for its similar taste to malt vinegar, often diluted from concentrate. Traditionalists may use brown malt vinegar, such as Sarsons.
Key Facts About Chip Shop Vinegar:
Non-Brewed Condiment:
It is technically not "vinegar" under UK law because it is not fermented.
Flavor Profile:
It is milder and less acidic than traditional malt vinegar, designed to complement rather than overpower the chips.
Alternative:
In some locations, brown malt vinegar or white distilled vinegar may be used.
Common Brands:
Besides non-brewed condiments, Sarson’s and Heinz malt vinegar are mentioned.

Yep, chip shop fish and chips with salt and vinegar (which technically isn't vinegar but everyone calls it that anyway). But tartar sauce is pretty common too.
I have always depended on the kindness of Strangers - and the bastards let me down!

Extremely greasy and like he smells bad.

Jason is looking a little greasy these days.
Ho Ho Ho

I prefer the acidity and sharpness of the malt vinegar. It's the perfect complement and neutraliser to the greasy fish.

It's kind of a British thing, isn't it? Us Yanks typically go for the tartar sauce rather than the vinegar and salt. I do love tartar sauce, but NGL, I'm open to either.

Yum. Now I want some battered deep fried fish filets.

I was brought up eating fried fish with vinegar and salt. It's delicious! Take it easy on the salt if you're worried about that. The vinegar cuts through the fat and takes the greasy taste away. Jason got it right!

Malted vinegar