Personal Pension - Siblings

Siblings:

One is a higher rate taxpayer (possibly 50%) and the other has a little earned income (self employment) and some investment income (easily falling within basic rate band).

Is it allowable for the wealthier sibling to contribute to a personal pension scheme for the poorer one and obtain tax relief at their highest rate?  If so, what is/governs the maximum contribution they could make on behalf of the poorer sibling and would it affect the latter’s own income tax position?  The contributions would not affect the lifestyle of the wealthier sibling.

Any advice would be most welcome.

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