St Helen's (skyscraper)

St Helen's (previously known as the Aviva Tower or the Commercial Union building) is a commercial skyscraper in London, United Kingdom. It is 118 metres (387 ft) tall and has 23 floors. The postal address is No. 1, Undershaft, though the main entrance fronts onto Leadenhall Street, in the City of London financial district.

The building was designed by the Gollins Melvin Ward Partnership in the international style: the stark rectilinear geometry and detailing of the building was influenced by Ludwig Mies van der Rohe and is somewhat reminiscent of his Seagram Building in New York City. It was built by Taylor Woodrow Construction as one of only four high-rise buildings in London using a top-down engineering design where the lower office floors are suspended from above rather than supported from below.

In 1992, the building was heavily damaged in the Baltic Exchange bombing carried out by the Provisional IRA, as a result of which it was substantially renovated.

The building was sold in 2003 by the Abu Dhabi Investment Authority to property developer Simon Halabi. In 2007, it was reported that Halabi was considering plans to demolish the building and replace it with a much taller tower, but this plan was not fulfilled. In 2011, it was reported that the building had been sold to an undisclosed Far Eastern private investor for £288 million. Plans for the site submitted in February 2016 feature a 310 m (1,020 ft) tall, 72-floor tower largely given to office space. In November 2016, planning permission was granted for the Trellis Tower, which will house up to 10,000 workers and which, upon completion, would have been the tallest building in the City of London and the second tallest building in the UK, after The Shard, but this design was ultimately discarded in favour of a quad-segmented tower revealed in August 2023.

Demolition of the building began in early 2025, following approval of the redevelopment plans in December 2024. Once demolition is completed, this will be the tallest skyscraper ever demolished in London. The only taller building ever to be dismantled in London was the Old St Paul's Cathedral after the Great Fire of London. It stood at an estimated 150 metres.