Migrants France Coquelles Calais Eurotunnel
Migrants walk in the proximity of the Eurotunnel rail terminal in Coquelles, near the northern French port of Calais, on August 2 2015 Getty

French police have said that migrants attempted to storm Eurotunnel's Calais terminal 1,700 times overnight as the stand-off between security services and the estimated 5,000 people in the area's makeshift camps continues. Police also said one officer was injured in clashes with migrants after he was hit by a stone. A police source told French magazine the Le Parisien that the member of the CRS riot control forces was struck in the head by a stone used to hold up security railings.

A Sudanese man, believed to have thrown the stone, was arrested in connection with the incident. Some 1,000 people were "pushed back" after being caught attempting to break into the terminal, with a further 700 found within the security perimeter.

It is the second time that migrants have attempted to storm the Channel Tunnel in their thousands. At the beginning of this most recent crisis at the border, more than 2,000 migrants attempted to gain access to Eurotunnel's freight entrance on the night of 27 July.

The numbers attempting to enter the terminal had initially fallen after the arrival of police reinforcements. France's Minister of the Interior Bernard Cazeneuve said an extra 120 police officers had been sent to Calais on 29 July. Police in Kent have highlighted the difficulties that authorities face in effectively tracking the migrant population in Calais, and how many make it through the tunnel.

French riot police detain migrant
French riot policemen detain a migrant near a fence as he attempts to access the Channel Tunnel in Calais on August 2 2015. Reuters

In a letter to a Commons Select Committee, Alan Pughsley, chief constable for Kent Police, said the exact figure is difficult to establish "due to the migrants using fake identities or giving false details to Border Staff". He added that information supplied by French authorities have "confirmed that through their own research 70% of migrants they process in the area of Calais leave the vicinity within a four-month period. Pughsley said: "They cannot ascertain whether these migrants leave to go elsewhere in France, or whether they enter the UK. Either way, their figures identify a transient migrant population."

Following the escalation of the crisis, David Cameron pledged to introduce further security measures around Eurotunnel on 31 July. The prime minister said following a convening of the Cobra emergency committee that the government would provide extra sniffer dogs and fencing for the French side of the border. The decision comes after the British government promised to provide £7m ($10.9m) of funding to bulk up security around the French port.

The operator of the Channel Tunnel, Eurotunnel, has made significant spending increases itself on security during the escalation of the migrant crisis. The group has spent €17 million in the last six months on security, more than the group spent in the whole of 2014.

The scenes of chaos at Calais over the last month have been as a result of a change in tactics by the 5,000 migrants camped near the town. In the past, individuals attempting to illegally enter the UK would attempt to board lorries before they entered the terminals. Now migrants are storming the terminals in vast numbers in the hope that some will get through. Nine migrants have died attempting to enter the UK over the last month.