Am I eligible? | Police Recruitment

I was aware of that id be considered an international student and it isn't an issue.ill be moving back when I'm 18 so my dad can't say anything, and my mother although i don't talk to her she lives in the UK so if push comes to shove i could live with her but that would never happen as i have my family i can stay with. also I'm planning on getting a job so finance will be fine as ill be staying with my grandparents and they would help me if i ever needed help. i know i could stay with them because she told me when she visited for a fortnight a couple weeks ago and she also told me when she visited in November.
my main concern with moving back is if i don't find a college program like the one here that i wanted to do.

IIRC the financial investigators in UK are called something like forensic auditors and for this you'll need a degree and lots of experience in auditing. I don't know about the UK equivalent of private investigators - I know they exist - or the legal requirements.
for what it's worth, if you are set on returning, then go back , live with your grandparents, get a job (if you can! difficult at moment) , and after 3 years when you will still only be 21, you can decide whether to join the police or go in some other direction. Only you can make that decision, here on BE we can only offer our opinions and/or experience. you can google for UK college courses to see if any fit your wants , but be aware, if there are any the chances of them being close to your grandparents may be slight!There are courses in criminology - I know because one of my nieces is looking at these, BUT they are all degree courses. You could, I suppose, take A levels once back in UK to see if you can qualify for a UK University, but again, you need the 3 years residence to avoid international student fees. Good luck in whatever you choose to do.

I've just done a bit of googling for you.
1. private investigators need a licence in UK and the conditions are quite strict including the required training.
2. The financial investigators job vacancies all call for years of experience and in most cases a degree , plus knowledge of the various acts relating to the job. Police, local authorities etc.

Any Canadian qualifications are likely to be next to useless in UK as they will not relate to UK laws.
If you are determined enough then you'll come back to UK and start your higher education here. you are young enough to have choices!

There are mutiple different, and completed unrelated, career paths that could be called a "financial investigator - some work for the police, and appear to be trained as a police promotion/specialty career path, then, as quiltman said, there are forensic accountant (perhaps auditor), which is a highly skilled and specialized job, and there are probably some lawyers who do something very similar. Then the banks have investigators, and so, I learned the other day, from someone on BE, that the DWP does, and of course HMC&R does too. I doubt that any of these career paths overlap, but all could reasonably be called "financial investigators".

However... Degrees for all new police officers under radical new plans - Telegraph

From what I observed of the police in Alberta, the criteria for entry can assumed to be lower than the UK.

Sounds like the OP should get a move on and apply to join the police as soon as turning 18.
Three years documented and vettable history of good behaviour and no serious contra-indictions being crucial.
A policeman can do Open University courses in crime studies on their own time while employed as a way to get ahead. OU degree too for that matter, no longer inexpensive but easily affordable if employed as a policeman.
Of course he will need to pass the physical fitness test.

Who will be paying your £15000 or so per year tuition fees?