Books fo Account

As per the Income Tax laws a person is required to maintain account books if his gross receipts/ turnover exceeds a specific amount.

Does he require to be ready with his books all the time during a F.Y. i.e. can IT authorities ask him to show books of account any time during the year or only after he has filed the return for a given year..?

e.g. can he be asked in F.Y. 2008-09 to show his books for the same financial year..?