What was the original name of this London building?

This building, currently (in 2021) known as "Tower 42," was originally designed as the headquarters of the National Westminster Bank. The detail of its construction illustrates this original purpose. Seen from above, the cross-sectional shape of the tower resembles that of the NatWest logo: three chevrons arranged in a hexagonal pattern.

The tower is located at 25 Old Broad Street in the Cornhill ward of the City of London. It was designed by Richard Seifert, engineered by Pell Frischmann, and built by John Mowlem & Co between 1971 and 1980. It was first occupied in 1980, although the formal opening by Queen Elizabeth II took place on 11 June 1981. The tower is 183 metres (600 ft) high, which made it the tallest building in the United Kingdom until the completion, ten years later, of One Canada Square at Canary Wharf.

Tower 42 is no longer owned by the National Westminster Bank: In 2011, it was bought by the South African businessman Nathan Kirsh for £282.5 million. Today the building is multi-tenanted and comprises prime office space and catering facilities, with restaurants on the 24th and 42nd floors.

Because of its purpose when constructed, the building’s original name was "The National Westminster Tower." However, it was always referred to colloquially as “The NatWest Tower.”