A level choices

So Im taking a level maths and physics definitely at a levels for an engineering degree, however im unsure whether I should take business (since it’s interesting), or biology (since im good at it and it’s a science) as my third subject. Which one should I do?

There's nothing stopping you from reading about business in a gap year or outside of uni/college (you don't need to study for it and take the exams if you don't want), but biology can be a pain to do outside of college if you need to do the practical assessments.

The other thing is you need to bear in mind that business is more of a vocational subject and not as academic as biology.
Biology can also be used for you to apply for bioengineering or for an engineering degree that requires maths + any science.

I don't know what the exact entry requirements are for the specific degree that you intend to do (engineering is not a small field), so I can't say whether the fact business is not considered much of an academic subject would hurt your chances.

Generally business A Level gives you a good foundation on how to run a business, so you won't be completely clueless if you start up your own company. Other than that, it's not much use for applications (job or uni).
Should you also want for any random reason to do a business related degree (not really recommended unless you want to go into academic research in business), you won't need business A Level just 3 A Levels in any subjects. Having said that, business degrees tend to repeat a lot of the material in Business A Level anyway.

I think the first thing I would do is to look through the entry requirements of the specific engineering degrees that you want to do first. You can then decide what to do next.

At uni I’m hoping to do aerospace engineering where the entry requirements are maths and physics so I’m mostly wondering what to do with that 3rd a level slot. Business being easier would give more time to focus on maths and physics however biology is more useful for applications etc but doesn’t apply much to my degree choice. It’s a strange situation so I’m just seeking some sort of advice from people who may have been in the same situation. I’m hardly interested in doing a biology related degree but more in a business related one. But I don’t want to waste that A level if unis don’t see it as acceptable for admission

So Im taking a level maths and physics definitely at a levels for an engineering degree, however im unsure whether I should take business (since it’s interesting), or biology (since im good at it and it’s a science) as my third subject. Which one should I do?

Then it wouldn't generally matter if you pick either subjects. However, as I said before, you would need to specify the specific degrees at the specific unis in order for me to check the entry requirements to see if they strictly are looking for academic subjects (unless you want to check this yourself).

If you're not sure, you can always email undergrad admissions at the engineering department of the unis that you want to apply for.

further maths would be good but if you dont want to do that choose biology as its a lot more respected than business (and you're good at it)

I would’ve loved to do further maths but I didn’t get the gcse grades for it sadly. I could choose chemistry too but I’m much better at biology than chemistry so I’m not too sure

Okay so my current thoughts:
aerospace engineering, Delft university of technology
Business management, Maastricht university
Business and economics, no seeked after university
Aeronautical engineering, Imperial college london
Economics, Oxbridge at best.

I understand that maths alone opens up many opportunities for study as does physics but biology if I do it is literally just because I’m good at it not because I want to do a study with it. Other a level options I could do is PE, chemistry, engineering (BTec which removes international options), or government and politics

Some exotic choices there.

aerospace engineering, Delft university of technology
https://www.tudelft.nl/en/education/admission-and-application/bsc-international-diploma/admission-requirements
https://www.tudelft.nl/en/education/admission-and-application/bsc-international-diploma/admission-requirements/diploma-with-additional-requirements#c106230
Should not matter which 3rd subject you choose

Business management, Maastricht university
No undergrad degree in business management found unless you can provide me with the link. See: https://curriculum.maastrichtuniversity.nl/education/bachelor/area_of_interest/business-economics-3421

Aeronautical engineering, Imperial college london
https://www.imperial.ac.uk/study/courses/undergraduate/aeronautical-engineering/
Probably biology, although it doesn't explicitly say

Economics, Oxbridge at best.
https://www.undergraduate.study.cam.ac.uk/courses/economics
https://www.undergraduate.study.cam.ac.uk/files/publications/economics_subject_requirements.pdf
I would stick to biology, but it's said that they do accept business.

Business and economics, no seeked after university
If you don't have a specific uni in mind, then I would leave this up to you. However, joint business degrees tend not to require specific subjects. If it's particularly quantitiative, it's likely going to require Maths. Otherwise, you should be fine with either subjects.

As you have A Level Maths and Physics, I don't see the point in doing the BTEC. I also don't recommend PE unless you want to borderline go into sports (in which case I would still recommend biology over PE). Chemistry and government and politics are fine alternatives if you don't want to do business or biology.