I assumed they probably would if both of a couple earned £150-250k, and it wasn’t their first house purchase so they had a reasonable amount of equity already, or had inherited and sold a parental home, or they worked in finance and got big bonuses, so only needed to cover 60% of the purchase price with the mortgage.
I agree nobody has a £3m mortgage on £250k household income, but you might well have a £1.5m mortgage on £400k household income (£150 + £250). And more people earn that than you might imagine (to be clear, I don’t! But a surprising number of nursery parents did).