37.—(1) The income from a trade, business or gainful occupation other than an occupation at a wage or salary shall be deemed to be whichever of the following the assessing authority considers more appropriate and practicable—
(a)the profits which have accrued or will accrue to the person concerned in respect of the period of calculation referred to in regulation 12(3); or
(b)the drawings of the person concerned.
(2) In calculating the profits under paragraph (1)(a)—
(a)the assessing authority may have regard to the profits of the last accounting period of such trade, business or gainful occupation for which accounts have been prepared; and
(b)there shall be deducted all sums necessarily expended to earn those profits, but no deduction shall be made in respect of the living expenses of the person concerned or any member of their family or household, except in so far as that person is wholly or mainly employed in that trade or business and such living expenses form part of their remuneration.