Four French police officers have been seriously injured during a 'savage ambush' by drunken UK-bound migrants in Calais.

One — an officer in a CRS riot control unit — was particularly badly hurt, after being hit repeatedly around the head with a large stone.

He was rushed to hospital following the organised attack in the port town on Monday afternoon.

Unsa police union released this photograph of a heavy stone used as a weapon to attack officers in Calais, northern France during an ambush by 'drunk' migrants

A riot cop was left with a bleeding gash above his eye, one of four police officers to sustain 'serious' wounds after the attack

A police source said: 'Our officers were drawn into a full-blown ambush, and four sustained serious wounds.

'The worst injury caused concussion and injuries that had to be treated in hospital. It was a savage ambush'.

Police were originally called to the Marcel Doret industrial zone just before 3pm, after being warned about a large build up of migrants who had broken in.

Many were trying to get on to the nearby ring-road, so as to try and get aboard lorries and other vehicles slowing down as they prepared to get on England-bound ferries.

A spokesman for the Prefecture that covers Calais said: 'Very drunk migrants threw missiles at them. One was wounded in the head, and taken to hospital in Calais.'

Police were called to the Marcel Doret industrial zone, where migrants attempted to board lorries and ferries bound for England

The Unsa police union meanwhile said the ambush was typical of the kind regularly seen in the town.

'The procedure is always the same,' said a union source. 'A small group of CRS intervenes to stop the offences of a small group of migrants.

'Then, very quickly, a hundred migrants leave the wood adjoining the industrial area and encircle colleagues who are forced to use weapons to repel the violent assaults carried out by the aggressors.'

Tear gas and baton charges were used by the police, but this did not stop 'a CRS captain being hit violently by a migrant armed with a huge stone. He was diagnosed with concussion.'

Police are under instructions to monitor all migrants in Calais, and to destroy any illegal camps.

This follows the razing of the so-called Jungle shanty town, where up 8000 men, women and children lived up until October 2016.

During a visit to Calais in January, French president Emmanuel Macon said the port would no longer be 'a secret gateway to England' for thousands of illegal migrants.

In a keynote speech, he said police and other agencies would stop them boarding trains, lorries and ferries heading for the UK, as they have been doing for at least two decades.

But it will come at a price to the British, who will be expected to pay more for security in Calais, and to accept greater numbers of migrants who cross the Channel to claim asylum.

'Everything is done so that illegal passage to the United Kingdom is not possible,' said Mr Macron. 'Calais must not be a secret gateway to England. The fundamental challenge is to ensure the security of the port of Calais and the Channel Tunnel'.

Mr Macron's confident prediction followed the town acting as a magnet to refugees and economic migrants from all over the world.

Beyond pouring millions into more police and extra security measures in Calais, Mr Macron said he wanted to reduce the amount of time migrants spent in France.

There are currently up to 500 migants congregating illegally in the Calais area, according to charity groups and other observers.

Many have complained about police brutality - something that the authorities deny is a serious problem.