A working musician is a business in the eyes of HMRC. The moment a performer earns their first fee from a gig, they are treated as self-employed. That means a Self Assessment tax return every year, and a bill that arrives months after the money was spent.
Most musicians learn about tax the expensive way: a surprise demand, too little set aside, a scramble to pay. The adviser's value is making sure it never works like that.
Start with the one number every taxpayer gets for free: the personal allowance. It is a tax-free band at the bottom of income, earn below it and no Income Tax is due at all; only profit above it is taxed. It is the same for an employee, a plumber, and a musician, and it resets every tax year. So the first question is not "how much tax will the client pay" but "how big is the slice the taxman never touches".
The second most powerful tool is one most musicians underuse: . Every £1 of legitimate business expense a client can document and claim reduces taxable profit, and therefore the tax bill. This is the "keep every receipt" lesson, and it actually has a number attached.