I'm always sad when I see signs with "No Lard No Pork No MSG" it's like all the good stuff taken away.

I just sang that to the tune of "Only Fools and Horses".

That's not a reason to be a fan. It's much unhealthier. Unless they are changing out the vegetable oil every day then it carries a much bigger cancer risk (due to aldehydes).

It is a reason to be fan if you are concerned about animal rights and the environmental impact of animal husbandry.

But, yes, in terms of personal health vegetable oil might not be better in any way. I know very little about that, and I have no reason to doubt your claim.

Are patties vegetarian? It's not like we're killing cattle specifically to render tallow.

Depends where in the UK you are. I guess fish patties prevalent, but in East Yorkshire potato patties with sage are also common. They're really delicious!

You're probably right that cows are not killed mainly for their tallow. Yet, let me try to illustrate why this can be off putting anyway (not trying to flame troll, but just to politely answer your comment): If your cat (or dog, or horse, etc) died in a traffic accident, would you cook a meal from it, even if it was not killed for that purpose? Some people respect the rights of all animals to the degree that they refuse to consider them as food; just like we do with our animal pets and other humans (even the humans we don't like, if any).

Interesting. Why? Halal definitely allows beef to be combined with potatoes.

This muslim chippy owner just told me that halal chippies never use beef dripping, when I asked about what oil they were using.

But as you say, it may not be because beef dripping as such is haram, but rather that the beef dripping that is available and used at traditional English chippies is not.

Honestly, I don't know why. I still look out for the halal sign on chippies, but I've also become better at telling just by the smell.

The beef has to be halal beef. In this context of using beef fat as an additive to other food, the beef fat has to be halal as well.

right, but the the gp said halal establishments always used vegetable oil instead of beef fat.

Perhaps there just isn't enough of a market for halal beef fat to make it worth the while of the carcass processing plants. They might sell it to be mixed with other beef fat.

I can think of another reason too: these chippie vendors might also want to cater to other people who don’t want to eat beef e.g. some Hindus. Some halal Indian restaurants in San Francisco do something similar: they serve halal chicken and lamb, but no beef.

tl;dr Vegetable oil ticks boxes for multiple sets of clientele.

That makes a good deal of sense. I'm a vegetarian, I appreciate it, but was merely surprised given that halal beef and halal beef fat exist. Thanks for these further speculations.