The name of this tower used to be just 'the Clock Tower'. In 2012 it was changed to 'Elizabeth Tower' as part of the celebration of the Queen's Diamond Jubilee.

The Elizabeth Tower is part of the Palace of Westminster located by the River Thames. The tower was designed by Augustus Pugin in a neo-Gothic style and was completed in 1859. It is one of the most easily recognised landmarks of London. The picture shows the view from the south bank of the Thames, near Westminster Bridge.

'Big Ben' is the name commonly given to the largest bell housed in the tower and forms part of the great clock of Westminster.

'Great Tom' is a bell in St Paul's Cathedral, in the City of London (not Westminster).

The Tower of London is a historic castle located on the Thames almost three miles downriver from the Palace of Westminster.

More Info: en.wikipedia.org