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When Europe Goes to the polls on 23 May, the right-wing campaign spearheaded by Italy's Matteo Salvini - leader of The League - could change the shape of European politics.

Salvini is trying to create a nationalist bloc that would be the second biggest force in the European parliament.

But where would that leave the centre-left or social democrats, who for decades were a natural party of government across Europe?

Three former leaders - Tony Blair, Matteo Renzi and Helle Thorning-Schmidt - offer their thoughts.

Our Diplomatic Editor Mark Urban reports.