Question: What is the official name of the tower, previously known as Clock Tower, next to which a proposed Thames Airport was to be built in the 1930s?

Context paragraphs:
Hopwood Clock Tower: The Hopwood Clock Tower, also known as Hopwood's Tower, but most commonly known as simply The Clock Tower, is a clock tower located in the centre of The Square in Palmerston North, New Zealand.  The tower is named after local businessman Arthur Hopwood who paid for it to be constructed in 1953.

Khan Clock Tower: The Khan Clock Tower was built in Colombo, Sri Lanka by the Khan Family of Bombay.  The Clock Tower is a popular landmark and marks the entrance to Pettah Market.  The Clock Tower was built in the early 20th century by the family of Framjee Bhikhajee Khan.  This Parsi family hailed from Bombay, India and also owned the famous Colombo Oil Mills as well as other business interests in Ceylon, as Sri Lanka was then called.

Proposed Thames Airport: Thames Airport was a proposed elevated airport during the 1930s that would have been constructed over the River Thames between Westminster Bridge and Lambeth Bridge.  Not much is known about the proposed airport, except that it would have had an elevator to bring people to the flight deck, as well as room underneath for a hangar.  It would have also been next to the nearby Big Ben and Palace of Westminster.

Big Brum: Big Brum is the local name for the clock tower on the Council House, Birmingham, England.  Built in 1885, the clock tower is part of the first extension to the original Council House of 1879 and stands above the Museum & Art Gallery.  The clock tower, Museum & Art Gallery and Council House were designed by architect Yeoville Thomason and form a single block.  The clock was donated by A. Follett Osler, a local pioneer in the measurement of meteorological and chronological data.

Beale Memorial Clock Tower: Beale Memorial Clock Tower is a clock tower located in Bakersfield, California.  It was a gift to the city; built by Truxtun Beale in memory of his mother, Mary Edwards Beale.  It was dedicated on April 4, 1904, and was built in the middle of the intersection of 17th St. and Chester Ave. When he was ambassador to Spain, Beale was inspired by a clock tower he saw there.  He hired architect Clinton Day to design it.

Clock Tower of Murshidabad: The Clock Tower of Murshidabad (locally known just as "Clock Tower" or "Ghari Ghar", also known as "Big Ben of Murshidabad") is a clock tower in the Nizamat Fort Campus in West Bengal, India.  The clock tower stands in the garden space between the Nizamat Imambara and the Hazarduari Palace; to its east, hardly a few feet away, is the old Madina Mosque and the Bacchawali Tope.

Birgu Clock Tower: The Birgu Clock Tower (Maltese: "It-Torri tal-Arloġġ tal-Birgu" ), also called the "Vittoriosa Clock Tower" and originally the Civic Clock Tower, was a clock tower in Birgu, Malta.  It was located in Victory Square, the city's main square, and it was a prominent landmark in Birgu and the rest of the Three Cities.  The tower was probably built in the Middle Ages, although some sources state that it was constructed in 1549.  It served as a watchtower since it had views over the Grand Harbour and the surrounding countryside, and it saw use during the Great Siege of Malta in 1565.  A clock was installed in the tower in the 17th century.

Clock Tower, Brighton: The Clock Tower (sometimes called the Jubilee Clock Tower) is a free-standing clock tower in the centre of Brighton, part of the English city of Brighton and Hove.  Built in 1888 in commemoration of Queen Victoria's Golden Jubilee, the distinctive structure included innovative structural features and became a landmark in the popular and fashionable seaside resort.  The city's residents "retain a nostalgic affection" for it, even though opinion is sharply divided as to the tower's architectural merit.  English Heritage has listed the clock tower at Grade II for its architectural and historical importance.

Mahboob Chowk Clock Tower: Mahboob Chowk Clock Tower is a five-storied architectural clock tower which was built in 1892 by Asman Jah, Prime Minister of Hyderabad.  The Mahbood Chowk area is considered to be an important part of Hyderabad architectural heritage.  The clock tower is erected in the midst of the small garden; it has four large clocks on its sides which enable the time to be seen from any direction.  The clock tower is designed is in the Turkish style.  The tower is located west of the Charminar, not far from Laad Bazaar.

Big Ben: Big Ben is the nickname for the Great Bell of the clock at the north end of the Palace of Westminster in London and is usually extended to refer to both the clock and the clock tower as well.  The tower is officially known as Elizabeth Tower, renamed to celebrate the Diamond Jubilee of Elizabeth II in 2012; previously, it was known simply as the Clock Tower.

Supporting paragraphs: Proposed Thames Airport Big Ben
Answer: Elizabeth Tower