Katherine Heron, Gavin Stamp and Philip Davies sign appeal to Sadiq Khan

The leader of the Skyline Campaign is appealing to London’s new mayor to halt all planning decisions on buildings over 20 storeys for six months.

A city-wide moratorium would create space for a public debate on the kind of capital people want, said architect Barbara Weiss.

Her petition calling on Sadiq Khan to freeze planning permissions for tall towers has been signed by 500 people including architects, academics and critics.

They include Katharine Heron, professor of architecture at Westminster University, who wrote: “The excessive number of high-rise buildings is unsustainable in terms of London’s infrastructure, and does not provide affordable homes.”

Dr Matthew Barac, an architect and lecturer in architectural history and theory at London South Bank University, wrote: “Our city is at risk of being ruined.”

Alexandra Valmarana, a conservation architect, wrote: “I am an architect with a vested interested in keeping London great. If we continue to grow in the same way, London will lose much of its uniqueness and ultimately its vibrancy as a global leader in planning, design, and sustainability for the future.”

Others who signed include architects Francis Terry and Leon Krier and Gavin Stamp who said the skyline had been transformed without its citizens’ approval or knowledge.

Research by New London Architecture has found there are 436 buildings of more than 20 storeys in the pipeline for London.

Philip Davies, former planning development director at Historic England, said it was essential for a moratorium to be placed on all tall buildings until a coherent urban design-led strategy had been drawn up – “or we risk destroying the very qualities that make London the pre-eminent world city”.

He added: “In spite of all the guidance and debate about tall buildings, there is still no effective spatial strategy for the capital identifying places where they are appropriate, or inappropriate, and the planning system has been reduced to speculative opportunism.

“Repeated studies have shown that there is no economic need for commercial tall buildings to sustain London’s position as a world city, while most of the residential tall buildings are buy-to-leave for absent overseas investors parking their capital in London. They have made little, if any, contribution to London’s overriding need affordable housing.

“The alternative is well-planned high-density, medium-rise buildings designed to reinforce London’s context and street architecture – a recommendation made by the Urban Task Force over 20 years ago.”

Michael Bach, urban planner and chair of the Kensington Society’s planning committee, said the key issue was what we want London to be like in eight years’ time.

“We need a rethink of tall buildings policy which will influence not only new applications but also the renewals of existing consents, culling the most-damaging, least-positive contributions and using new buildings to take us in the direction of a new long-term strategy.

“What is in the ‘pipeline’ is not inevitable or even likely to be built. The mayor needs to reshape our vision for London. Without Ed Lister we can change direction,” he added, referring to Boris Johnson’s deputy mayor for planning.