By Miranda Alexander-Webber CALAIS, France (Reuters) - Migrants massed around the entrance to the Channel Tunnel said on Thursday they would keep trying to sneak across to Britain, undaunted by the arrival of 120 extra riot police on the French side. A police officer said the number of migrants trying to enter Britain eased slightly overnight compared to earlier in the week, with about 800 migrants around the site and some 300 intercepted by police. Some 3,000 migrants live around the tunnel entrance in a makeshift camp known as "The Jungle", making the northern French port one of the frontlines in Europe's wider migrant crisis alongside Italian and Greek islands used an entry point for those crossing the Mediterranean from Africa or the Middle East.