Debate has raged since William IV

How to fill the empty plinth in Trafalgar Square has been a topic of impassioned debate ever since it was built in 1841. It was originally intended as the site for a figure of William IV, but owing to a lack of funds, the statue was never made.

Thereafter, agreement could never be reached on whom or what should be given the honour of a permanent home in the square.

The plinth stands eight metres tall on the National Gallery side of the square. Charles Barry, who had the task of completing the square's design after its original architect died, included an elevation of a statue on each plinth to act as a backdrop to Nelson's Column.

Two years ago, a committee headed by Sir John Mortimer decided to make the plinth a permanent showcase for contemporary art.

First came Ecce Homo, a marble resin life-size figure of Christ by Mark Wallinger. Next up was Bill Woodrow's bronze sculpture of a book tangled in the roots of a tree. Then, in June last year, a £300,000 sculpture designed by Rachel Whiteread called Monument was installed - a 20-tonne replica of the concrete plinth, placed upside down on the original. Resembling a Fox's glacier mint, critics derided it as "ridiculous" and "completely out of place".

Over the years, suggestions have included Victorian adventurer Cecil Rhodes, who was vetoed by the Royal Fine Art Commission, Sir Winston Churchill, whose statue already stands at the other end of Whitehall, and Earl Mountbatten, blown up by the Provisional IRA in 1979.

Responsibility for the square rests with the Greater London Authority and Mayor Ken Livingstone has said he wants statues more "relevant" than the politically incorrect Imperial war heroes on two of the other plinths. He has suggested the former South African President Nelson Mandela as one possibility.

Already in the square are an equestrian figure of George IV, Sir Henry Havelock, chosen for his role in quelling the Indian Mutiny of 1857 and General Sir Charles Napier, a hero of the Peninsular War against Napoleon.