Nearly 10,000 plants, many rare and threatened, will live at Temperate House in Kew Gardens when it opens to the public on May 5 after five years of restoration.

Dubbed the “greatest glasshouse in the world”, its “long journey back to magnificence” involved 400 staff and contactors and took 1,751 days to complete.

The restoration of the impressive structure- opened in 1863 and still the largest Victorian glasshouse in the world- was made possible by a £15 million grant from the National Lottery, and required scaffolding the equivalent length of the M25.

Richard Barley, director of Horticulture at RBG Kew, said: “Over the past few months, I have watched as some of the world’s rarest plants finally reach their home.

“And what a home it will be - a glistening cathedral, the new glass allowing the sun to stream in, the ironwork restored to its glossy best.

“The Temperate House will be for everyone.

“From young to old, for budding gardeners or aspiring artists, for those making a pilgrimage from great distances, and for our local community, we hope every visitor will see plants in a new light.”

Originally designed by world-famous architect Decimus Burton, heritage architects Donald Insall have updated and modernised key features to enable the building to function as a contemporary working space.

More than 69,000 individual elements were removed from the building and cleaned, repaired or replaced, including the replacement of 15,000 panes of glass.

Lead Aimée Felton, lead architect on the project, said: “The restoration of the Temperate House has been a complex and immensely rewarding project, recalibrating contemporary understanding of Victorian architecture and the development of past innovations.

“New glazing, mechanical ventilation systems, path and bedding arrangements all took their founding principles from Decimus Burton’s own drawings, held within Kew’s archives.

“The time it will take for the newly propagated plants to reach maturity will offer visitors a full and unobstructed view of the incredible metal skeleton in all its glory: a cutting-edge sanctuary for plants.”

Ros Kerslake, chief executive of the Heritage Lottery Fund, which made the restoration possible, said: “We know from speaking to National Lottery players the value they put on protecting and understanding the natural world – a value that also makes the Royal Botanic Gardens, Kew one of our best-loved visitor attractions.

“This extraordinary glass structure has always epitomised all that is wonderful about these gardens – it is a magical place with a massive heart, which makes a huge contribution to biodiversity and natural heritage.”