Parmesan has something called ‘protected characteristics’ which are very strictly controlled. If a cheese is described as Parmesan then it has to have those characteristics - one of which is the use of calf rennet.
It’s why on the supermarket shelves you’ll sometimes find products described as vegetarian hard cheese next to the Parmesan.
Unfortunately restaurants have been slow to understand this and the Vegetarian Society has been campaigning for years to try to raise awareness in professional kitchens.
I’ve been to some really nice places where the only vegetarian main course contained Parmesan and the puddings were full of gelatine. I might have well taken sandwiches.
Pizza Express has been really good providing vegetarian (and more recently vegan) cheese options. That makes me trust them. I feel that they know what they’re doing and if they describe something as suitable, I can eat it.
I honestly hope this doesn’t read like a lecture. I don’t mind what anyone else eats and certainly don’t mean to suggest that what I eat is better than the choices anyone else makes.
It’s important to me, though, and eating out is a big trust issue. If a chef puts Parmesan in a dish, will he add Worcester sauce too? Will he use the same spoon to stir meat dishes?
I’ve lived with a vegan for a decade and been veggie the same amount of time. People use “Parmesan” in the same way they use “hoover”. I’m willing to trust a restaurant that has gone to the extent of saying “(vegan) parmesan” on their menu knows the difference