Sycamore & Co is the auditor of Fir Co, a listed computer software company. The audit team comprises an engagement partner, a recently appointed audit manager, an audit senior and a number of audit assistants. The audit engagement partner has only been appointed this year due to the rotation of the previous partner who had been involved in the audit for seven years. Only the audit senior has experience of auditing a company in this specialised industry. The previous audit manager, who is a close friend of the new audit manager, left the firm before the completion of the prior year audit and is now the finance director of Fir Co. The board of Fir Co has asked if Sycamore & Co can take on some additional work and have asked if the following additional non-audit services can be provided: (1) Routine maintenance of payroll records (2) Assistance with the selection of a new financial controller including the checking of references (3) Tax services whereby Sycamore & Co would liaise with the tax authority on Fir Co’s behalf Sycamore & Co has identified that the current year fees to be received from Fir Co for audit and other services will represent 16% of the firm’s total fee income and totalled 15·5% in the prior year. The audit engagement partner has asked you to consider what can be done in relation to this self-interest threat. In relation to the composition of the current audit team, which of the following correctly identifies the fundamental principle which is at risk and provides an appropriate safeguard?