More than half the country's adult population was expected to watch the two hour confrontation, which was to be carried live on France's two biggest television channels.

Televised debates have been held between the finalists in every French election since 1974 -- except in 2002 when Jacques Chirac refused to meet far-right leader Jean-Marie Le Pen.

Both the Sarkozy and Royal camps know that the head-to-head encounter could be crucial in determining the choice of millions of uncommitted voters.

Nearly seven million people chose defeated centrist Francois Bayrou in the first round of the vote on April 22, and the second round campaign has focussed on capturing his electorate.