Do Law and Business if you want to study Business, but don't think that it will give you any advantage for corporate/financial law (indeed, it may give you a disadvantage. Business is not taken particularly seriously by law firms and you will miss out on some advanced subjects relevant to business law such as company law, commercial law, intellectual property, civil jurisdiction etc. because you won't have a lot of optional modules left to once you have studied the compulsory core law modules).
Have heard of people who have changed course at a late stage. Best to ask Birmingham ASAP if this is what you want to and hope that they still have space on their Law and Business course.