The Economist recently released a video explaining why London is the most expensive city in the world to build in. One of those reasons included unexploded bombs.
View this video on YouTube
The Blitz by the German Luftwaffe during World War saw thousands upon thousands of bombs dropped on London.
Many of those bombs still remain unexploded, and are still dangerous 69 years after the war ended.
Removal of these bombs is both costly and time consuming, making construction costs extremely high.
The webpage bombsight.org shows how many bombs were dropped, and where they were dropped over the course of the war. Zooming out really gives some perspective on the sheer number of them.
Another reason for London’s high building costs is its complex underground rail system.
The system consists of traditional subway routes, and several other lines both for public and government use.
Building on over these criss-crossing lines adds added costs to modify infrastructure to build on up, or around these lines. Not to mention that the London Underground is notoriously complex.
The video mentions that London's layout also contributes to its high building costs.
Narrow streets and alleyways make it difficult and expensive to get equipment in. Oddly laid out neighborhoods also mean buildings have to sometimes have unique designs so they can fit correctly.
According to the video it costs, up to a fifth more to build a new office in London than it does in New York or Hong Kong. The Economist also states that leasing an office in the West End costs about twice as much as leasing an office on New York's Madison Avenue.
In spite of the growing costs London doesn't appear to be shrinking anytime soon.
According to the most recent census central London saw a 20% population increase from 2001 to 2011.
London is also expected to add around another million people by 2021. So high costs or not, space in Central London is in demand, and it seems as if people and contractors will be willing to foot the bill to continue to build in the city.