internal audit and external audit

It is only considered acceptable to provide internal audit services where specific safeguards are put in place including a requirement that the audit firm should ensure that the audit client acknowledges its responsibilities for establishing, maintaining and
monitoring the system of internal controls.

It is also important to minimise self-review threats by ensuring that staff who perform internal audit functions are not involved in the external audit of that client.

7 years

The current guidelines do not now mention 10% and only mentions 15% with respect to public interest clients:

Where an audit client is a public interest entity and, for two consecutive years, the total fees from the client and its related entities …represent more than 15% of the total fees received by the firm …the firm shall disclose to those charged with governance of the audit client the fact that the total of such fees represents more than 15% of the total fees received by the firm, and discuss which of the safeguards… it will apply to reduce the threat to an acceptable level, and apply the selected safeguard.
:

If an accountancy firm has total revenue of $12 million, 15% of that is $1.8 million. The firm is therefore not allowed to have more that $1.8 million total fees from one client for more than two consecutive years without various safeguards.