6In any circumstances in which apart from this paragraph a person would—
(a)under section 72 of the [1970 c. 9.] Taxes Management Act 1970 be assessable and chargeable to Class 4 contributions as trustee, guardian, tutor, curator, or committee of an incapacitated person in respect of the profits or gains of a trade, profession or vocation ; or
(b)by virtue of section 114 of the Act of 1970 be assessed and charged to such contributions in respect of profits or gains received or receivable by him in the capacity of trustee,
such contributions shall not be payable either by him or by any other person.