(1)For the purposes of this Chapter “long-life asset” means plant or machinery which—
(a)if new, can reasonably be expected to have a useful economic life of at least 25 years, and
(b)if not new, could reasonably have been expected when new to have a useful economic life of at least 25 years.
(2)“New” means unused and not second-hand.
(3)The useful economic life of plant or machinery is the period—
(a)beginning when it is first brought into use by any person for any purpose, and
(b)ending when it is no longer used or likely to be used by anyone for any purpose as a fixed asset of a business.