I have been advised by the Revenue Commissioners that, if for any year of assessment a claimant proves that he-she maintains at his or-her expense any person being:— (a) a relative or a relative of a spouse, who is incapacitated by old age or infirmity from maintaining himself-herself, or (b) his or his spouse's widowed mother, whether incapacitated or not, or (c) a son or daughter who resides with him/her and on whose services he-she, by reason of old age or infirmity, is compelled to depend, and, in each case, being a person whose total income from all sources for that year of assessment does not exceed specified limits, he-she shall be entitled, in respect of each person whom he-she so maintains, to a deduction of £110.
As the son of the taxpayer in question does not fall into any of the above categories he is not entitled to the allowance.