On owner-occupied lending the lender is underwriting your business. It works from filed accounts and current management figures, adds back directors’ remuneration and one-off costs where they are evidenced, takes out the rent you will stop paying once you own the building, and then tests whether what is left services the loan at a rate higher than the one you will actually pay.
On investment lending the lender is underwriting the income. It looks at the passing rent, how long the lease has to run, whether there is a break clause, and what the tenant’s own accounts say about their ability to keep paying it. Your accounts matter far less than theirs.
It is worth knowing which assessment you are in before an application goes anywhere, because the document list is different, the loan to value is different, and so is the list of lenders worth approaching.