Planning applications for mega-basements in Hammersmith and Fulham has rocketed, new figures released by the Labour London hopeful have revealed.

Labour's London Mayor candidate Sadiq Khan has promised to tackle the growing problem of the extensions, also known as iceberg developments, and revealed applications in Hammersmith and Fulham more than doubled in a five-year period between 2010 and 2015.

The borough also had the highest number of planning applications in 2015 in the 12 London boroughs looked at. The figures show mega basement planning applications rose from 378 to 826 - an increase of 448, or 118.5%.

Neighbouring Kensington and Chelsea, saw a rise of six over the same period, from 182 to 188, representing a 3.3% increase. However, the Royal borough became the first authority in the country to introduce tight restrictions on basement developments with more than one storey in January 2015.

In Westminster, where the council introduced plans to tackle ‘underground epidemic’ of mega-basements in February 2015, applications rose from 84 to 117, a rise of 24.5%.

Extensions can undermine foundations

Basement extensions several storeys below the ground have become increasingly popular in some of the capital’s most expensive neighbourhoods as home-owners attempt to increase their living space without infringing strict planning controls.

They have led to the creation of huge underground extensions with the extra space earmarked to accommodate private cinemas, spas and swimming pools.

But the excavation work often cause misery to neighbours because of noise and dust, and has led on some occasions to the foundations of buildings being undermined .

Across the 12 boroughs examined, there was an overall increase of 66%. Now Mr Khan, who heads to the polls on May 5, is pledging to strengthen the London Plan to ‘give greater protections for residents affected by large-scale basement excavation works’.

He said: “The growth of super basements has been really damaging for communities in Hammersmith and Fulham and across London.

“They cause disruption, noise and annoyance for thousands of Londoners, blighting neighbourhoods for months on end. People have also expressed real concerns about the impact on mega-basements on the foundations of surrounding buildings.

“As Mayor, I’ll act to give greater protection to local residents in London.

“I’ll amend the London Plan to limit the size of so-called mega basement extensions, and give neighbours greater protection from the noise, dust and disruption major works on this scale can cause to households and communities.”

The figures do not represent the number of mega basements built during the period, but solely the planning applications but before the councils.

Borough No of applications 2010 No of applications 2015 Difference 2010-2015 % difference 2010-2015
Camden 47 41 -6 -12.77
Greenwich 8 16 8 100
Hackney 200 345 145 72.5
Hammersmith & Fulham 378 826 448 118.52
Islington 289 338 49 16.96
Kensington & Chelsea 182 188 6 3.3
Lambeth 374 621 247 66.04
Lewisham 84 115 31 36.9
Southwark 440 615 175 39.77
Tower Hamlets 133 169 36 27.07
Wandsworth 323 837 514 159.13
Westminster 94 117 23 24.47
Total 2552 4228 1676 65.67