The Allahabad High Court has ruled that in case of private assesses, the Commissioner can refer the matter to an officer to collect the material for the purpose of audit. However, audit can be performed only by Chartered Accountants / Cost Accountants.
The relevant extract from the judgment is as follows:

"Rule 5-A, sub-rule (2) states that every assesses shall, on demand, make available to the officer authorized or the audit party, records, trial balance and income-tax audit report, if any. So here, the officer will demand the documents just to facilitate the correctness of books of accounts and ultimately, the audit will be conducted by the Audit Party headed by the Chartered Accountant/Cost Accountant, as the case may be, deputed by the Commissioner."