For years, migrants trying to make their way from France across the Channel to the UK have been stuck in the Calais "jungle" migrant camp, often living in squalid conditions. And for years, politicians have promised to deal with the situation, to no avail. Now, with the French presidential campaign in sight, Calais has seen a flurry of visits in recent days, first and foremost by President Hollande and then by his predecessor - and possibly also his successor - Nicolas Sarkozy.