London’s skyline is to be transformed over the next decade with a record 510 tall towers, more than 20 storeys high, planned or under construction. The total is up from 455 towers in the pipeline in 2016, according to research from the industry forum New London Architecture (NLA) and real estate consultancy GL Hearn.

Construction has started on 115 towers, also a record. Over the past two years, work started on more projects than in the preceding five years combined.

Twentytwo, formerly nicknamed “the Pinnacle” and then “the Stump” after work stalled, will be – at 62 storeys or 278 metres – the tallest building in the City of London when it is completed next year. However, in the 2020s it will be overtaken by 1 Undershaft, nicknamed the Trellis, at 290m.

Two of Europe’s tallest residential towers will be the 233-metre Landmark Pinnacle on the Isle of Dogs and the 235-metre Spire London, also in Canary Wharf. Both are expected to be completed by 2020. But they do not come close to the Shard, which, at 310 metres, remains the tallest building in Europe.

The report also recorded signs of a slowdown. Last year 40 tall building projects were under way, a 25% drop on 2016, and 18 were finished, down 30%. Projects now typically take three to four years from start to finish rather than two to three years as before.

The number of applications for new towers last year was down by 10% from 2016 and by 35% from 2015, when an application for Greenwich Peninsula was made involving more than 40 tall buildings.

Peter Murray, the NLA chair, said the slowdown was to be expected. “The uncertainties created by Brexit are causing projects to be postponed, while higher stamp duty introduced by George Osborne in December 2014 continues to impact on the market.”

The planned towers could provide 106,000 new homes by 2030, while the mayor of London has called for 66,000 new homes a year. Half of the planned towers (252) are in east London, while the second-biggest cluster (99) is in central London.

Almost a third of the entire pipeline is in outer London, in zones three, four and five. In Croydon, the world’s tallest modular tower, containing more than 300 build-to-rent flats, has received planning consent.