Section 41 of the Act confers authority upon the Commissioner to issue permits "upon and subject to such terms and conditions as he deems fit with respect to the amount or rate of the fee to be paid in respect of the permit " Section 44 of the Act deals with permit fees and provides inter alia: - "(2) In respect of a permit, the fee payable (b) with respect to the carriage of goods, may in the discretion of the Commissioner, be - (i) a fixed amount; (ii) the sum of the amounts fixed by the Commissioner for each and every vehicle in respect of which the permit is issued; or (iii) an amount calculated at a rate not exceeding the sum of the products obtained by multiplying, in respect of each and every vehicle in respect of which the permit is issued - (a) three pence; by (b) the load capacity of the vehicle expressed in tons (including fractions of tons to the nearest hundredweight); and by (c) the number of road miles on which goods are carried on the vehicle pursuant to the permit, but shall not in any event exceed an amount calculated as prescribed by sub-paragraph (iii) of this paragraph (b)." Sub-section (3) makes it clear that the amount "calculated as prescribed" by (b) (iii) is the maximum fee payable and that, if a fee in excess of the maximum should be determined, the determination is invalid as to the excess. The fee demanded from Turner was, it seems, calculated strictly in accordance with the formula in (b) (iii). Although the fee was not imposed by the Act itself but was fixed by administrative authority two steps removed from the Act, yet since it involved no departure from the legislative authority conferred by the Act, it is possible, for the purpose of considering whether it can be a duty of excise, to regard it as a tax imposed by statute. To do this enables the appellants' principal contention to be considered free from the complications that would arise if we were to regard the fee in question as it strictly is, viz. one determined by the delegate in the exercise of a general administrative authority conferred upon the Commissioner by the Act. On the basis stated, the constitutional problem before us is whether, if the fee were imposed by the Act, it would be a duty of excise. If not, it is not necessary to go any further.