(1) In this section -
"wear and tear allowance" means an allowance made under section 284 otherwise than by virtue of section 285;
"normal wear and tear allowance" means such wear and tear allowance or greater wear and tear allowance, if any, as would have been made to a person in respect of any machinery or plant used by such person during any chargeable period if all the conditions specified in subsection (3) had been fulfilled in relation to that chargeable period.
(2) Where for any chargeable period during which any machinery or plant has been used by a person no wear and tear allowance or a wear and tear allowance less than the normal wear and tear allowance is made to such person in respect of the machinery or plant, the normal wear and tear allowance shall be deemed for the purposes of subsections (3) and (4) of section 284 to have been made to such person in respect of the machinery or plant for that chargeable period.
(3) The conditions referred to in subsection (1) are -
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