The European Union’s repeated crises over how to reform its institutions might eventually make it necessary to create a “multi-speed Europe”, with the most pro-integrationist countries at its heart, Nicolas Sarkozy, France’s president, said on Thursday.

“Perhaps one day, unfortunately, we will have to have that multi-speed or multi-tier Europe. But it could only be a last resort. Let’s think before we leave anyone behind,” Mr Sarkozy told the European parliament.