For the organized visitor, London's many other high points, including the Post Building, One New Change and the Tate Modern, offer wonderful free vistas that are worth the effort required to gain admission, if only to see familiar sites from unfamiliar angles.

Ian Mansfield, editor of the London exploration and information website Ian Visits, told China Daily that viewing platforms are nothing new in the city.

"The (62-meter-high) Monument, commemorating the Great Fire of London, opened in 1677 and was the original London viewing platform, but after that not much happened until the BT Tower's rotating restaurant opened in 1965, but that shut in 1980 over security fears," he said.

"I think the creation of the London Eye for the Millennium triggered people's expectations that they should have some sort of public access to views."

Both the Greater London Authority, which runs the wider London region, and the City of London Corporation have encouraged developers to include public provisions, but Mansfield said that it was "just a bit of coincidence that we've had so many so tall buildings go up in such a short time that we now have a cluster".

The new platforms offer visitors views that could only otherwise be seen from a low-flying aircraft, and Mansfield said that opening them has been part of a deliberate policy to give the City a life beyond working hours.

"A City official once said to me that they didn't want it to be like Manhattan, which is dead out of (office) hours, and I think it worked - the City certainly feels busier," he said.

But while busier streets may be welcome, there is concern over the increasingly busy skyline.

In 2014, architect Barbara Weiss was one of the founders of the Skyline campaign, which aims to protect London from domination by excessively tall, overbearing buildings.

"I was dismayed by the realization that too many beautiful historical buildings were being demolished in the name of regeneration, only to be replaced by ones consistently inferior in terms of design, materials and craftsmanship," she told Architects Journal.

"As I watched with great consternation, a gray army of lift cores started morphing into enormous incarnations, drastically and permanently altering the city's skyline."