Hundreds of migrants headed for Britain yesterday just 24 hours after Andy Burnham claimed the plan to stop small boats 'is working'.More than 700 migrants are thought to have attempted to cross the Channel on one of the busiest days so far this year.Shadow Home Secretary Chris Philp was told by one French officer that they had orders not to intervene, as the Tory MP spent the day monitoring departures from a beach in the north of the country.Gendarmes stood by as more than 100 migrants gathered in shallow waters before struggling aboard one overloaded inflatable bound for the UK.Ruthless people traffickers also appeared to have adopted a new tactic, mounting simultaneous boat departures from multiple locations up and down the French coast.On Tuesday the new Prime Minister defended the Government's handling of the Channel crisis, saying: 'The numbers can fluctuate but, overall, boat crossings are down, down quite significantly year on year. So that does suggest the plan is working.'However, the scale of yesterday's crossings – which has yet to be officially confirmed by the Home Office – could indicate that a significant downturn in migrant numbers may be coming to an end.According to unofficial estimates about 570 migrants had reached Dover by yesterday evening. Last night there were still three dinghies making their way across the strait. Hundreds of migrants headed for Britain yesterday just 24 hours after Andy Burnham claimed the plan to stop small boats 'is working'. Pictured: Migrants were seen running towards a smugglers' boat in Gravelines, northern France, on Wednesday Gendarmes stood by as more than 100 migrants gathered in shallow waters before struggling aboard one overloaded inflatable bound for the UK According to unofficial estimates about 570 migrants had reached Dover by yesterday eveningIt was not clear whether they would cross the mid-point of the Channel in order to be picked up by Border Force by midnight, in time to be included in the day's tally.One of the boats deployed by traffickers yesterday was understood to have set off from Belgian waters earlier in the day.The first were believed to have arrived in the early hours of yesterday, just hours after the PM voiced his confidence in the current measures.Later, Mr Philp confronted a gendarme on Hardelot-Plage, south of Boulogne, and asked: 'Why have you allowed the migrants into the water? Why haven't you stopped them?'The French officer shrugged and replied: 'Our order is to let them go like that. We just have to say to them 'Don't do that,it's dangerous'. At one point Mr Philp waded into the sea just feet away from waiting migrants, who he said were predominantly young men from sub-Saharan Africa.He confronted someone on the dinghy who appeared to be a people smuggler and told him: 'You're committing a number of criminal offences. You're attempting to illegally enter the United Kingdom.' The Tory frontbencher said the scenes he witnessed proved the failure of Home Secretary Shabana Mahmood's new £662million deal with the French government. Ms Mahmood claimed the three-year agreement, signed in April, would clamp down on dinghy departures with enhanced beach patrols and tougher tactics.The Home Office said at the time that the deal would 'slash crossing numbers'.