For the purposes of sub-section (4) of section 12, the amount of turnover or turnover of purchases arising in the tax period in the case of a sale or purchase occurring -

(a) by means of an installment sale or hire purchase of goods made in the tax period, is the total amount of the sale price that will be due and payable under the agreement, including the amount of any option fee paid or that may be payable;

(b) by the transfer of a right to use goods, not being a hire purchase agreement or installment sale agreement, is the proportion of the sale price that is due and payable during the relevant tax period;

(c) by means of transfer of property in goods (whether as goods or in some other form) under a works contract executed or under execution in the tax period, is the consideration received or receivable by the dealer for such transfer of property in goods (whether as goods or in some other form) during the relevant tax period.