Liability to pay octroi by the Government–Production of a certificate that the property imported will be used for official purpose only goes to the matter of levying the tax called octroi. The rule does not cast any duty upon the tax collector to find out the purpose of the Government as· to how they will use their goods. It is the Government or their officer–in–charge of the goods imported into the octroi barrier to declare how they will use it, for official purpose only or for any other purpose. Certificate to this effect regarding the use of the property is mandatory. Bangladesh vs Mis. MF Limited 44 DLR (AD) 166.

The sole criterion for determining whether a government property is intended for ‘Consumption or use for official purpose only” is a certificate signed by a Gazetted Officer of the Department concerned. The certificate must accompany the property of the Government when brought into the Octroi area.
An absolute or mandatory rule is the substance as against a directory rule which is a shadow, the former goes to the root of a matter; the latter touches merely the fringes or branch of the matter. The Secretary, Ministry of Food, Food Division, Government of Bangladesh and others Vs. M/S. M. F. Limited, 13 BLD (AD) 145.