Nicolas Sarkozy has underlined his determination to block foreign takeovers of strategic French companies by fiercely condemning last year’s acquisition of Arcelor, Europe’s biggest steel group, by Lakshmi Mittal, the Indian billionaire, as a “waste”.

The presidential frontrunner voiced a sharp protectionist twist to his industrial policy at a campaign rally in Lille on Wednesday night. His comments are likely to shock many of his admirers in the US and UK, who see him as France’s best hope for reform.