If you view it as the cost of overlaying a new local transport service on to the existing infrastructure of many of the world’s biggest cities, $25bn doesn’t seem like that much money. But as the amount of money raised by two private start-ups that have less than a dozen years between them, the number is truly extraordinary.

That is roughly how much money has now been poured into the coffers of Uber and Didi Chuxing, the US and Chinese ride-hailing app companies, following tit-for-tat announcements in recent days.

Their investors are going to need a strong stomach. Both companies have shown a willingness to engage in expensive subsidy battles to win market share. Given the huge potential returns — Uber takes a 20-25 per cent slice of each fare — there is every reason to think that this fight will continue for some time. Much more money will need to be raised before it is over.