(1) In this section -
"trading company" means a company whose business consists wholly or mainly of the carrying on of a trade or trades;
"investment company" means a company (other than a holding company) whose business consists wholly or mainly in the making of investments and the principal part of whose income is derived from the making of investments;
"holding company" means a company whose business consists wholly or mainly in the holding of shares or securities of companies which are its 90 per cent subsidiaries and which are trading companies.
(2) This section shall apply if -
(a) within any period of 3 years there is both a change in the ownership of a company and (either earlier or later in that period, or at the same time) a major change in the nature or conduct of a trade or business carried on by the company, or
(b) at any time after the scale of the activities in a trade or business carried on by a company has become small or negligible, and before any considerable re