Finance Act 1949

2 Subject to the provisions of this paragraph, no initial allowance shall be made to a person in respect of any machinery or plant in charging the profits or gains of a trade, profession, employment, vocation or office, if it appears that, during the period during which the machinery or plant will be used by him for the purposes of the trade, profession, employment, vocation or office, sums which are in respect of, or take account of, the wear and tear to that machinery or plant occasioned by its use for those purposes and do not fall to be taken into account as his income or in computing the profits or gains of any trade, profession, employment, vocation or office carried on or held by him are, or are to be, payable to him directly or indirectly by the Crown, or by any government or public or local authority, whether in the United Kingdom or elsewhere, or by any person other than the person carrying on or holding the trade, profession, employment, vocation or office:

Provided that where the sums referred to in this paragraph are in respect of, or take account of, part only of the wear and tear therein referred to—

(a) the preceding provisions of this paragraph shall not apply; but

(b) the amount of the allowance shall be reduced to such extent as may be just and reasonable having regard to all the relevant circumstances of the case.