(1) Subject to such conditions as the Commissioners may prescribe or otherwise impose, a relief from mineral oil tax shall be granted on any mineral oil that is shown to the satisfaction of the Commissioners -
(a) to be intended for use, or to have been used, for purposes other than motor or heating fuel,
(b) to be intended for use, or to have been used, for chemical reduction or in electrolytic or metallurgical processes,
(c) to be mineral oil in respect of which the Minister thinks it proper to repay or remit mineral oil tax or part of that tax to the extent that the Minister thinks proper,
(d) to be intended for use, or to have been used, by a manufacturer in the production of mineral oil,
(e) to be heavy oil which is intended for use, or which has been used, in aircraft engines during testing and maintenance of those engines, or
(f) to be intended solely for use, or to have been solely used, to produce electricity, where that electricity is subject to electricity tax under section
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