Why do you need a separate business bank account?

For limited companies it is effectively a necessity because the company's money is legally not yours. For sole traders it is not usually a legal requirement and is still the single highest-return administrative decision you can make early.

For a limited company. The company is a separate legal person, and its money belongs to it. Paying personal expenses from the company account creates a director's loan, generates tax consequences, and undermines the separation that limited liability depends on. Most banks' personal account terms also prohibit business use.

For a sole trader, business and personal money are legally the same — but mixing them causes real problems:

Bookkeeping cost. Separating personal and business transactions from one account is slow, error-prone and something accountants charge for. A separate account removes that work entirely.

Tax accuracy. Deductible expenses are far easier to identify and evidence, and you claim more because you stop missing things.

Enquiry risk. If a tax authority examines your affairs, a mixed account means your personal spending is in scope as well. A clean separation limits what is being looked at.

Visibility. You cannot tell whether a business is working if its money is mixed with your household spending — which is how people run unprofitable businesses for years without noticing.

Professionalism, since clients paying an account in a business name is a small credibility signal.

How to do it properly:

Pay yourself deliberately, by a regular transfer, rather than dipping in. Treat it as a salary or drawings.

Set aside tax as income arrives — a separate savings account holding a fixed percentage prevents the single most common cause of small business failure, which is spending money that was always the tax authority's.

Use one card for business, and connect the account to bookkeeping software.

Keep a buffer for lumpy expenses.

Choose the account on the right criteria: monthly fee, transaction charges, cash and cheque handling if you need them, integration with your accounting software, and whether you will need borrowing later.

General information, not financial or tax advice.