Professors Reinhart and Rogoff were embarrassed by a spreadsheet gaffe. Now statisticians within the Japanese government are smarting, after a private-sector economist pointed out errors that led them to overstate weakness in the economy during the fourth quarter last year.

In an announcement to the Japanese press club on Tuesday evening, the Cabinet Office said that a miscalculation of the value of trade in services between October and December meant that nominal gross domestic product was reported as shrinking by 0.3 per cent, rather than the true figure of 0.1 per cent.

With Britain’s economy bumping along the bottom and official data prone to large revisions, analysts have been on the lookout for indicators of regional and national recovery.

Until now, no one spotted a good set of figures, quietly collated at the Health and Safety Executive. Cranes puncturing the skyline are the most visible indicator of economic dynamism and have often been used to gauge the heat in economies as diverse as Dubai or China and the torpor of Tokyo.

The HSE started requiring the operators of tower cranes – used for new office buildings, infrastructure, larger residential blocks and big public sector projects – to register their addresses in 2010, providing an invaluable snapshot of the building industry in action.

The results show a remarkable degree of concentration in London and its surrounding counties, signifying a gulf between the optimism about a prosperous future for the capital and pessimism in the rest of the UK.

With London home to only one in eight people in the UK, it has seen more tower cranes notified to the HSE than all the rest of the UK put together. Almost eight in 10 cranes were in London, the southeast and the east of England.