The field of mould-breaking, job-creating, tree-hugging, consensus-seeking, debt-cutting, Europe-doubting politicians has grown more crowded in France's presidential elections. Now there are three.

For several weeks, Nicolas Sarkozy, the boisterous presidential candidate from the ruling UMP party, and Ségolène Royal, the elegant Socialist party challenger, thought they were the only electoral party in town. But François Bayrou, the rustic leader of the centrist UDF party as famous for his tractor as his political ideology, has rudely gatecrashed their bash.