an establishment engaged during the necessary period wholly or mainly in the engineering construction industry; and

an establishment (not falling within sub-paragraph (a)) at or from which persons were employed during the necessary period in any activities such as are mentioned in paragraph 1(c) of the Schedule to the industrial training order (related and administrative etc. activities) (but subject to paragraph 2 of that Schedule).

unless sub-paragraph (b) applies, a period (which need not be continuous) consisting of a total of 27 or more weeks falling within the base period; or

in the case of an establishment that started to carry on business in the base period, a period (which need not be continuous) falling within the base period consisting of a total number of weeks exceeding one half of the number of weeks in the part of the base period starting on the day on which business was commenced and ending on the last day of the base period.