(a) that the sum of—
(i) the amount payable in respect of that claim; and
(ii) the total amount in respect of which certificates have previously been given in relation to the contract under that subsection;
does not exceed the total amount to be paid under the contract; and
(b) that the head of administration or authorised officer is satisfied that the sum of the amounts referred to in subparagraphs (a) (i) and (ii) does not exceed the value of the supplies that have been executed, furnished or performed under the contract on the date to which the claim relates.