St. Helen's (previously known as the Aviva Tower or the Commercial Union building) is a commercial skyscraper in London. 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.
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, 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 May 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 May 2011 it was reported that the building had been sold to an undisclosed Far Eastern private investor for £288 million.
St. Helen's may be demolished, to replace a new skyscraper.