139. Agreements entered into after the introduction of this Act.—

Where a contract is concluded after the introduction of this Act and the contract does not include  a provision relating to value added tax and supplementary duty—

(a) such contract price shall be deemed to include the value added tax and supplementary duty (if any) payable on the supply; and

(b) the supplier under the contract shall be required to pay the value added tax and supplementary duty (if any) imposed on  supplies made under the contract, whether or not the supplier include those taxes in the price for such supplies under such contract.