This section applies where a person carrying on a trade who for a consideration disposes of, or of his interest in, any assets ("the old assets") declares, in his return for the chargeable period in which the disposal takes place—
Until the declaration ceases to have effect, section 152 or, as the case may be, section 153 shall apply as if the acquisition had taken place and the person had made a claim under that section.
The declaration shall cease to have effect as follows—
On the declaration ceasing to have effect in whole or in part, all necessary adjustments—
In this section "the relevant day" means—
Subsections (6), (8), (10) and (11) of section 152 shall apply for the purposes of this section as they apply for the purposes of that section.