In this Act a "trade union" means an organisation (whether temporary or permanent)—
which consists wholly or mainly of workers of one or more descriptions and whose principal purposes include the regulation of relations between workers of that description or those descriptions and employers or employers' associations; or
which consists wholly or mainly of—
constituent or affiliated organisations which fulfil the conditions in paragraph (a) (or themselves consist wholly or mainly of constituent or affiliated organisations which fulfil those conditions), or
representatives of such constituent or affiliated organisations,
and whose principal purposes include the regulation of relations between workers and employers or between workers and employers' associations, or the regulation of relations between its constituent or affiliated organisations.