The London Olympics of 1908 cost ￡20,000. The budget for the austerity games of 1948 was ￡750,000. The current estimate for the cost of the Olympics in 2012 is ￡11bn.

This escalation in price is extraordinary, but today big schemes seem to imply very big budgets. The earliest underground railway lines in London – and the world – cost half a million pounds a mile to build. Roughly, you can assume that average prices in Britain multiplied by 10 between the Victorian era and 1960, and by another factor of 10 in the 50 years following. The cost of the Victoria line, built in the 1960s, had risen in line with general inflation and came in at about ￡7m per mile.

This, however, now seems an astonishing bargain. A decade later, the Jubilee line cost ￡36m per mile to build and its extension in the 1990s 10 times as much. The tunnels for Crossrail, the newest underground railway connection in London, are budgeted at almost ￡1bn per mile. The explosion of the cost of mega projects appears to be a phenomenon of the past 50 years. The Forth Bridge, an engineering marvel that connects Edinburgh with Fife, was completed in 1890 at a cost of ￡3.2m. The parallel road bridge erected in the 1960s cost ￡19.5m – broadly in line with general inflation. The budget for a third crossing is currently ￡1.6bn.