A light-hearted vox-pop asking London couples to name their biggest money disagreement — candles, haircuts, a Tesla — might seem far removed from the concerns of professional property investors. But scratch beneath the surface and these everyday squabbles are a useful, if unscientific, barometer of something far more consequential: the financial compatibility, or lack of it, that increasingly determines whether couples can buy, hold and manage property together at all. With joint mortgage applications now accounting for the majority of first-time buyer completions and cohabiting couples the fastest-growing family type in the UK, according to the Office for National Statistics, how partners handle a £40 haircut says more than one might think about how they will handle a £400,000 mortgage.