(1) Notwithstanding section 142(1), in the case of a person who -

(a) has attained the age of 18 years and has not attained the age of 25 years,

(b) is not a person referred to in section 142(1)(a)(ii) (as amended by section 20 of the Social Welfare and Pensions Act 2007), and

(c) is not entitled to an increase in respect of a qualified child,

the scheduled rate of jobseeker's allowance shall be the weekly rate set out in column (2) at reference 1(c) in Part 1 of Schedule 4, (as inserted by section 11(a) of the Social Welfare and Pensions Act 2009) increased by the amount set out in column (3) of that Part opposite that reference for any period during which the claimant or beneficiary has a qualified adult, subject to the restriction that the claimant or beneficiary shall not be entitled for the same period to an increase of allowance under this subsection in respect of more than one person.