With its skyline about to expand further upward, the city may one day look back on the Shard as the thin end of a vertical wedge

London's relatively clear skyline, once dominated by St Paul's Cathedral and, later, by Canary Wharf, the Gherkin and the Shard, is likely to get an awful lot more crowded over the coming years, with almost 250 tall towers proposed, approved or already under construction.

A survey by the New London Architecture (NLA) thinktank suggests that 236 buildings of more than 20 storeys could be on the way, 189 (80%) of which are intended to be residential blocks. Eighteen are planned as office developments, eight as hotels and 13 are due for mixed use, while one tower is to be an educational institute.

According to the study, which is based on local authority figures, 48% of the towers have been approved and another 19% are under construction. Thirty-three of the 236 will be between 40 and 49 storeys high; 22 will have 50 or more storeys.

At the heart of the new tower boom is Tower Hamlets, in east London, which is to be home to 23% of the new buildings. Projects in east and central London account for 77% of the total, although south London also faces significant vertical development. Between them, Tower Hamlets, Lambeth, Greenwich, Newham and Southwark will have 140 of the 236 towers.

Peter Murray, director of the NLA, said the survey had been prompted by remarks made by the London mayor, Boris Johnson as he announced his revised housing strategy at the end of last year.

"He said that we've got to build 42,000 new houses every year, but it won't mean towers are 'popping up all over London', as he put it," said Murray.

"But then we started looking at some of the statistics coming in from various boroughs as to the sorts of buildings they were giving permission to, and we realised that actually it does mean that: just like in the 1960s, when we had to build a whole lot of houses, we are going to go higher than I think a lot of people in London had imagined."

And, judging by his comments, higher than Boris imagined as well.

Looking west from the City, how London will look with the addition of planned towers. Illustration: Hayes Davidson/Jason Hawkes

The survey is the thinktank's way of attempting to gauge the effect the new towers will have on the London skyline and the shape of the city as a whole.

"I've got nothing against towers at all, but we need to understand what the impact is," said Murray. "We need to make sure we have a planning system that really is fit for purpose to properly do what planning is supposed to do: to provide a vision for the city in the future and to control the way that development takes place in a reasonable manner."

Murray, who believes the current system could do with some "beefing up", points to the huge pressures on the Greater London Assembly and local authorities to deliver more housing at a time of very high land prices. Faced with such prices, developers are understandably keen to build high, he says. The situation is further compounded by increasing demand for housing in London from the east Asia, where tall buildings have long been part of the urban landscape.

Sir Edward Lister, London's deputy mayor for planning, said a strategic approach was required to balance the protection of the city's skyline with the need to house 1 million more people and create more than 500,000 new jobs over the next few years.

"What we can't do is try to impose some kind of freeze on the skyline and suspend the capital in stasis," he said.

"The key issue in any discussion of London's skyline is whether a building makes a positive contribution to London's urban realm, protecting the things we value about our city while helping us meet the challenges of growth and ensuring the continued prosperity of London and Londoners."

The NLA, which is now examining people's attitudes to tall buildings, believes the public is more receptive to high-rise buildings than it once was.

"There's a greater acceptance of towers because generally the architecture is more interesting than it was in the 1960s, when there was a general antagonism towards taller buildings," said Murray. "I think buildings like the Gherkin – which people generally like – have restored people's faith in the ability of architects to put up buildings that can enhance the skyline rather than damage it."