Every taxable person, including one claiming the relief, must still
register for Corporate Tax and submit a return for each tax period, since the election itself is made on that return. What the relief removes is the need to calculate taxable income under the full Corporate Tax rules, along with the obligation to prepare detailed financial statements in most cases.
Businesses electing the relief also give up other reliefs and deductions for that period, including tax loss relief and net interest expenditure carry-forward, and they lose the ability to claim those later even if they stop claiming Small Business Relief.