“all material placed before them and, on that material, come to a decision which is one which is reasonable and not arbitrary as to the amount of tax which is due. As long as there is some material on which the commissioners can reasonably act then they are not required to carry out investigations which may or may not result in further material being placed before them.”
“primary task of the Tribunal to find the correct amount of tax, so far as possible on the material properly available to it, the burden resting on the taxpayer.”