Westminster City Council has introduced a levy on the construction of basement extensions.

Homeowners in the Lonodn borough wishing to extend their property underground will now have to pay an extra £8,000 on average, up to £30,000 for larger developments to fund the council’s new ‘subterranean squad’ of basement monitors.

The levy is as part of the council’s new code of construction practice, clearly sets out best practice for building sites such as basements. The code will also be rolled out over the coming months to cover larger developments in the city.

Over the last five years Westminster City Council has received on average 150 applications a year and has seen a trend towards more ‘iceberg’ basements where homeowners dig down two or more storeys.

The new rules include planning controls limiting basements to a single storey and no more than 50% of total garden land.

The new ‘subterranean squad’ will:

• make sites coordinate their deliveries to reduce the impact on residents
• check that developers are keeping neighbours informed
• enforce stricter working hours so as to avoid noisy works at inconvenient times such as Saturday mornings
• provide a point of contact for residents with complaints – with the power to enforce against overly noisy sites under statutory powers
• monitor the level and impacts of traffic to sites
• police development sites of over 10 residential units, or over 1000 m² commercial floorspace.

Westminster City Council deputy leader Robert Davis, cabinet member for the built environment, said: “We are sticking up for local residents, many of whom have found the explosion of basement development in recent years hellish. It is right that those who want to build basements should contribute to this new service, which will work to help mitigate the negative impacts.

“Westminster City Council supports the right kind of growth and is not against all basement development, but they must be carried out in a way that is considerate to local residents and the environment.”

The new powers will apply to basements that gained planning permission from August 2016 onward, and other major development schemes from September.