Firstly, you will need A grade A-levels in Maths and biology as a start. And that means the same at GCSE level.
Secondly, you will need a lot of work experience, experience of being with and looking after animals, in order to even be seriously considered by the universities. A friend’s DD has just started at vet school and as well as decent grades she was expected to have spent at least three years getting decent exposure to animals e.g. volunteering at animal shelters, on a family member’s farm, work experience at an actual vets etc, and only about 20% of those who apply are actually accepted on to the course, regardless of their grades.
Secondly, work experience is important not only to get on to the course, but also so you’re aware of what you’re getting into.
It’s not all treating sick animals and making them better, it’s euthanising a litter of puppies because the owner couldn’t be bothered to get the bitch spayed and doesn’t want to find homes for them.
It’s putting a healthy dog to sleep because the owners are moving abroad.
It’s attending cruelty cases where an animal has been so badly neglected or treated that euthanasia is the only fair thing to do.
It’s aiding an animal to give birth to dead young because they weren’t looked after properly during pregnancy or even because they were just unlucky. And the list goes on.
And I agree with PP, it’s really not true that you can achieve anything you put your mind to. There’s nothing wrong with trying, but sometimes it just isn’t possible, and if you don’t think about the pitfalls before you start so you can see how realistic you are being, then you’re potentially setting yourself up for huge disappointment later.