§ 25. Paragraph 6 of Part II of the principal Schedule shall have effect as if at the end there were added the words "and every full-time employee of that company who is chargeable to tax in respect of his employment under Case I of Schedule E must be entitled to participate in the scheme to a reasonable extent if he is not less than twenty-five years old and has been a full-time employee of that company for a continuous period of not less than five years."