4Where owing to the recent commencement of a trade or business there have not been three pre-war trade years, but there have been two pre-war trade years, the pre-war standard of profits shall be taken to be the amount of the profits arising from the trade or business on the average of those two years or, at the option of the taxpayer, the profits arising from the trade or business during the last of those two years, and where there have not been two pre-war trade years, but there has been one pre-war trade year, the pre-war standard of profits shall be taken to be the profits arising from the trade or business during that year ; and where there has not been one pre-war trade .year, the pre-war standard of profits shall be taken to be the statutory percentage on the average amount of capital employed in the trade or business during the accounting period.
Where the trade or business is an agency or business of a nature involving capital of a comparatively small amount, the pre-war standard of profits shall be computed by reference to the profits arising from any trade, business, office, employment or profession of any sort, whether liable to excess profits duty or not, carried on by the agent or other person before his new trade or business commenced as if it was the same trade or business ; but only to the extent to which the income from the former trade, business, office, employment or profession has been diminished.