No, you don't need a degree in finance, economics, or accounting to go into finance.
Unfortunately there is no universal definition for a role as a commercial finance manager. Looking through a sample of job listings, it seems being a qualified accountant would be sufficient:
https://careers.dyson.com/en-gb/job-description/commercial-finance-manager/JR22720https://www.sodexojobs.co.uk/jobs/job/Commercial-Finance-Manager/56574https://www.michaelpage.co.uk/job-detail/commercial-finance-manager/ref/jn-102023-6207225https://www.reed.co.uk/jobs/commercial-finance-manager/51933511?source=searchResults&filter=%2Fjobs%2Fcommercial-finance-manager-jobshttps://www.reed.co.uk/jobs/commercial-finance-manager/51761482?source=searchResults&filter=%2Fjobs%2Fcommercial-finance-manager-jobsThe most commonly quoted accounting qualifications are ACCA, CIMA, and ACA. ACCA and ACA generally ask for passes at A Levels, whereas CIMA doesn't have any requirements to start.
Do note: to become fully qualified in any accounting qualification, you would need the minimum number of years of qualified work experience, under the same person that is qualified in the qualification e.g. you cannot become CIMA qualified whilst working under an ACCA accountant, it needs to be a CIMA qualified accountant; similar with ACCA and ACA.
One company is interestingly is asking for a degree in a relevant area, which I am not entirely sure what they mean.
There are other professional accounting qualifications such as ICAS, CAI, AIA, etc. (see:
https://en.wikipedia.org/wiki/British_qualified_accountants), but the above tend to be the most popular. ACA would be my recommendation because you can move into more careers and fields with it than CIMA and ACCA. The only drawback of ACA is that it's not as internationally recognised as ACCA, so if you intend to work in another country chances are it's either not recognised (so you would need to study another professional accounting qualification suitable for the country or do one that's internationally recognised in most countries such as ACCA) or you have to convert the qualification to the local professional accounting qualification (if they accept it) + do the necessary work experience to qualify.
Do note: although they are all more or less the same, ACA is regarded as a better qualification than ACCA. In your case, I don't particularly matters, but still ACA trumps ACCA.
Do also note: just because you are qualified in one accounting body, it does not exclude you from qualifying in another e.g. after qualifying in ACA for example, you can then do 4 more papers to qualify under ACCA (after paying a big fee for all of your exemptions) if you then do the necessary qualified work experience under an ACCA accountant.
As you did not specify which other countries you intend to work in, I would leave it up to you how far ahead you want to plan and whether you want your qualification to be valid in your home country. If you want more detail, then you would need to detail what your intentions are.
Do also note, just because you can work as a commercial finance manager in the UK without a degree, it does not necessarily mean you won't need one in your home country. As I don't know which country you intend to work in and what the requirements to be a commercial finance manager is in your home country, I would leave this up to you to research.
So I overall don’t need Econ and accounting?Not if you intend to work in the UK. From the look of things, just 3 very good A Levels in any subjects.
A degree in economics is great if you intend to become an economist or teach economics, but generally that's the sort of jobs that requires such a degree. You don't need an accounting degree to work in accounting in the UK (you would need one or sufficient number of accounting classes in your degree in the US and Canada though).
what I am overall afraid of is if I take the physics and something else, it would definitely be harder so I am scared to not get good grades.As the line of work that you want to get into doesn't really depend on you studying specific subjects, I would focus on doing the subjects where you would get the highest grades, much to my disappointment.
If you can get the highest grades in maths, fm, and economics, then take those subjects.
If you do have a specific career in finance that you really want, then it's a good idea to look into it now as opposed to leaving it a few years down the line. If you want to look through the job profiles yourself, see:
https://nationalcareers.service.gov.uk/job-categories/business-and-financehttps://www.careerpilot.org.uk/job-sectors/finance-accounting/job-profileshttps://www.prospects.ac.uk/job-profiles/browse-sector/accountancy-banking-and-financehttps://www.life-pilot.co.uk/job-sectors/finance-accounting/job-profiles