11. Where an element of a person’s retirement provision ceases to be payable by one source but –
(a)responsibility for that element is assumed by another source, income from both those sources shall be treated as income from the same source, or
(b)in consequence of that element ceasing, income of a different description becomes payable from a different source, that income shall be treated as income of the same description from the same source as the element which ceased to be payable.