14. Subject to article 15:
(a)every fee shall be paid by means of a cheque or postal order crossed and made payable to H. M. Land Registry;
(b)where the amount of the fee payable on an application is immediately ascertainable, the fee shall be payable on delivery of the application;
(c)where the amount of the fee payable on an application is not immediately ascertainable, on delivery of the application there shall be paid on account of the fee such sum, being not less than the minimum fee payable in accordance with Scale A in Schedule 1, as the applicant may reasonably estimate to be the fee payable and there shall be lodged therewith an undertaking to pay on demand the balance of the fee due, if any.