The vast majority of the unfunded borrowing is paying for the energy bill subsidies, at least up until the next general election (and who knows what will happen after that). The IMF have also specifically warned against those blanket subsidies, not that you'd know this from the BBC's coverage of their statement for some reason, and there are really fundamental economic reasons why they're likely to tank the pound and force the BoE to put interest rates up to do with balance of payments and the global supply of fossil fuels. This is probably less obvious from the media coverage because most of the reporting on the size of those tax cuts seems to quote a hypothetical figure for how much they'd be worth in 2025-6.