There is long-standing case law which supports the contention that such things must be income or capital. There is no “neither” option. As they’re apparently a pensioner there’s also no provision for the capital to be treated as income. Unless the OP has some facts to which we have to be privy this is straightforward capital for me.
The dictionary definition of “income” has little relevance here. The benefits definition is quite specific with regard to frequency and periodicity.
