Even before either has opened their mouths, tonight's clash, to be broadcast to millions, is a powerful symbol of the political earthquake that has already changed France's political landscape.

Until two weeks ago no candidates debate had ever been held before the first round of a French presidential election.

This time all 11 candidates, rather than just the five front runners, will be taking part, creating both a historic and colourful piece of political theatre. 

Even by the standards of French politics, which tend to include a vast spectrum of ideological hues, the panel will be diverse - it will include three representatives of parties on the right, four drawn from the left and four "independents". Sparks are sure to fly.