Section 640 Exemption under section 639 where income withheld

(1) This section applies if—

(a) an individual is entitled to both of the following—

(i) a pension or allowance mentioned in section 639 (“pension A”), and

(ii) any other pension or allowance (“pension B”), and

(b) the whole or a part of pension A is withheld because of the individual's entitlement to pension B.

(2) In such a case, an amount of pension B equal to the withheld amount of pension A is treated for the purposes of section 639 as part of pension A.