One of the most popular museums of modern art in the globe is about to become larger to give a bigger picture, literally, of the world of contemporary but controversial design.

And in keeping with its headline-making exhibitions, London’s Tate Modern gallery plans to construct a new, breathtaking extension – a series of gigantic glass boxes about 70 metres high.

Visitors approaching the museum will see the extraordinary building appear as a stack of Cubist-like rectangular areas shaped into a glass pyramid. The extension will make for a big increase in the gallery’s existing floor space and cater for more than one million extra visitors a year. It is planned to be ready in 2012, in time for the London Olympic Games and even greater visitor interest.

Tate Modern opened in 2000 in the redundant Bankside power station across the River Thames from St Paul’s Cathedral, and now attracts more than five million visitors a year – making it one of the capital’s top tourist attractions.

Sir Nicholas Serota, Director of the Tate galleries, said the extension was necessary to cope with the number of visitors. “Tate Modern was originally designed to receive 1.8 million visitors a year. Now it receives more than four million,” he said. He added that there had been profound changes in the art scene since Tate Modern was designed in the mid-1990s. It now needed to cater for photography, film and new media, as well as “stretching the boundaries” of its collecting  policy to include art from Asia, Africa and Latin America. “We need the space to show that work,” he said. “In addition, the expectations of visitors have been dramatically transformed over the last ten years. They expect a different kind of experience.”

The team that produced Tate Modern – premier UK design group Arup and Swiss-based architects Jacques Herzog and Pierre de Meuron – have joined forces again for the extension project. The ultra-modern 10-storey glass extension would increase the gallery’s size by 60 per cent, providing ten galleries of varying sizes and shapes, learning spaces, two shops and six cafes, bars and restaurants. Two performance areas to be fitted in the space that once housed the power station’s oil tanks, include a 400-seat auditorium. The space will be left as “rough and authentic” as possible.

Tate’s planners want facilities for young people to be central to the development, with learning and visitor engagement at its heart. The project is expected to cost 215 million pounds sterling, financed by private and public money, and its designers believe it will become an “iconic new landmark for London”.

The extension will create 7,000 square metres of exhibition space and more educational facilities. It will enable much more of the Tate’s collection to be brought out of storage. A roof terrace would provide views across London, and the pyramid would look out onto a new piazza where 1,000 trees would be planted.

Design and construction group Arup believes that the transformed Tate Modern is destined to become a cultural campus. “Arup is providing a full suite of design services, as well as transport and environmental design,” said a spokesperson.

Arup will also apply its expertise in internal environmental design to achieve the optimum internal conditions for the galleries, applying low-energy and sustainable methods where possible, including reusing waste heat and installing energy piles connected to the building structure, moderating hot and cold weather conditions.