The Tulip – a 305.3-metre tall tower topped with a viewpoint and rotating gondolas designed by Foster + Partners – is planned to be built alongside the Gherkin in London.

Foster + Partners has submitted its design for the tower, which would become the tallest structure in the City of London, for planning permission.

If approved, the tower could begin construction in 2020, with an opening date planned for 2025.

Visitors would ascend the London viewpoint, which has been designed to look like the petals of a bulbous tulip flower on top of a thin stem, to reach the viewpoint, attractions and an education centre.

Internal glass slides and spinning gondola pods fixed to the three sides of the facade would provide novel vistas over the city. Sky bridges would run between the observation decks, and the Tulip would have a bar and restaurant with 360-degree views.

The design recalls a hybrid of the rotating pods of the London Eye attraction and the panoramic restaurant that once sat at the top of the BT Tower.

The Tulip would be built on the plaza of the Foster + Partners-designed, Stirling Prize-winning 30 St Mary Axe, better known as the Gherkin.

Foster + Partners designed the project for the J Safra Group, a privately owned banks and investment holdings company that owns the Gherkin.

A slim concrete shaft would provide a durable support for the steel-framed observation building glazed with high performance glass.

At it's widest point the observation deck would be 34.5 metres, with the concrete shaft would measuring just 14.3 metres in diameter.

"Continuing the pioneering design of 30 St Mary Axe, the Tulip is in the spirit of London as a progressive, forward-thinking city," said Norman Foster.

"It offers significant benefits to Londoners and visitors as a cultural and social landmark with unmatched educational resources for future generations."

An education centre located within the Tulip would offer 20,000 free places a year to local state school children to use the facilities, said Foster + Partners.

The centre would teach national curriculum topics, with interactive guides available to teach all visitors about London's history.

At the base a two-storey entrance pavilion with a rooftop garden would stand next to a "pocket park". Alongside green walls this would increase the green surface area of the site by 8.5 times, said the architects.

Photovoltaic cells would generate on-site energy, and the Tulip would be heated and cooled using less polluting zero combustion energy.

Foster + Partners won the 2018 Stirling Prize for their Bloomberg HQ office building, which was designed to be the "world's most sustainable office".

Six of the 13 new skyscrapers due to transform the City of London skyline by 2026 will include observation decks, including the 289.9-metre-high 1 Undershaft by Eric Parry Architects.

Renderings are by DBOX for Foster + Partners.