If players could loan money from the bank like say you take a £1 million loan then you pay the loan back every day with a little bit of money every day.also make a 10%-25% intrest rate the bigger the loan the more intrest %

Bigger the loan the less interest I say. Maybe interest rates start at 25% and as you increase a "credit score" or other unknown stat via on time payments and amounts withdrawn, then interest rates will decline. 

it should have collateral or have a way to check if the person have the ability to repay the said loan. This would lead to disaster if someone suddenly decided to create tons of accounts just to get loans from the bank without proper checking.

I like the idea, I even like the idea of being a loan shark. Don't pay back on the agreed terms, automatically get bountied daily until you do. But realistically, managing this for abuse, if it were from the bank, would be a nightmare.