A successful modern city needs to evolve its built environment in response to the ever-changing needs of its population. Good jobs, high-quality housing, world-class arts and culture and excellent health care can’t happen in outdated leaky old buildings. With London competing on the world stage with Paris and New York, there’s never been a greater need for high-quality and flexible offices, apartment blocks and theatres.

But a successful modern city can no longer afford to provide these spaces simply by replacing old buildings with new ones. The environmental cost of demolish and rebuild is simply too great. In Westminster alone, we estimate the carbon currently released from demolitions and redevelopments is the equivalent of heating 35,000 homes a year. As we move to our ambition of a net zero city by 2040, this is no longer acceptable. We need change.

Fortunately, everybody I meet in the real estate business, from architects to financiers, is up for the challenge of delivering a built environment that generates little or no greenhouse gas emissions. The industry has innovated more in the past five years than the last 15 as engineers learn more about how to use and re-use existing buildings in new and exciting ways.

The Derwent London project on Greencoat Place, for example, refurbished a six-storey Victorian warehouse into a 32,000 sq ft of high-quality office space with a design by Squire and Partners. This is a great demonstration of how well-planned retrofit schemes can reimagine an existing building, respecting its character while creating use for a new generation. Successful retrofit of the building took its energy rating from E to B, while retaining the cast iron columns and brickwork famous to the Victorian era. The building now emits 64 per cent less carbon.

Another example is IKEA. The retailer has refurbished the former Topshop on Oxford Street, replacing gas-fired boilers in this Grade II-listed structure with air source heat pumps to power the building with renewable energy.

With the real estate industry serious about transforming the existing building stock into low or zero carbon emission buildings, we need to make sure that planning policy is supporting the transition. Building owners, developers and financiers all need clear and consistent policies that outline the parameters of acceptable development at a time of climate emergency. Uncertainty, as we have today following Michael Gove’s quixotic decision to refuse the new Mark & Spencer building on Oxford Street, increases risk and results in postponed projects. Yet with every retrofit delayed, our chances of hitting carbon reduction targets diminishes.

At Westminster, we will shortly begin consulting on new policies we believe will deliver the certainty needed to stimulate a virtuous circle of retrofit investment and carbon reduction. We will be encouraging owners to refurbish their buildings as the default option.

However, we recognise that there are circumstances where demolition and rebuild will still be the best approach. Our policy will be retrofit-first, not retrofit only. Some buildings, such as multistorey car parks, simply cannot be repurposed for the modern world. We also know that affordable housing, good quality healthcare and safe places for our young people to socialise are lacking in modern London. Our retrofit approach will always consider that some new buildings will be worth their cost in carbon to deliver value to our communities, and this will be considered when assessing planning applications.

Where demolition and rebuild is supported by our new policies, we plan to introduce the concept of carbon budgets. Essentially, new buildings will need to meet targets for tonnes of CO₂ emitted per square metre of floorspace, taking into account the embodied carbon in the old building but reduced by any materials recycled. We would expect the average embodied carbon emissions for development in Westminster to be well below the current 850-1,000kg CO₂/m².

Nevertheless, we expect retrofit to be the best solution for the vast majority of buildings in Westminster. It’s the right thing for the planet and makes good business sense. Buildings can be refurbished, and new occupiers can be found more quickly and with much less risk than a demolition and rebuild.

But we know that planning policy needs to support the business case for retrofitting, which is why our new policies will be favourable towards modest upwards extensions, where they both facilitate a wider retrofit of a building and help deliver the City Plan’s growth objectives.

With our retrofit-first approach, we hope landlords will refurbish their buildings to the latest low-carbon, sustainable standards, providing the high-quality floorspace needed to maintain London as a global destination and to support good jobs and economic growth. Just as your most sustainable item of clothing is the one already in your wardrobe, the materials already in the building are the ones least damaging to the planet.

Geoff Barraclough is cabinet member for planning and economic development at Westminster City Council