Socialists and allies held on to power France's big four cities - Paris, Marseille, Lyon and Lille - on a local election night that offered hopes for mainstream parties in next year's presidential elections. The new aspirants of the far-left and far-right also made gains – notably in Nice for an ally of Marine Le Pen and Roubaix in the north for the France Unbowed (LFI) party. But the big lesson of the evening was the failure of alliances between mainstream left and LFI, with voters turning to the centre and right in long-time Socialist Party (PS) strongholds like Clermont-Ferrand and Brest. On the contrary, in cities like Paris, Marseille and Lille – where incumbent Socialists steered clear of the far-left because of accusations of sectarian anti-Semitism in its ranks – left-wing administrations were comfortably returned.…