Channel people smugglers are using smaller boats as decoys to pave the way for vessels carrying more than 80 migrants, Border Force sources have revealed.

The smaller boats are put to sea from different locations on the coast of northern France at the start of the day to tie up French rescue vessels before larger boats are launched later.

The bigger vessels, which can travel further, are being put to sea further down the 150 miles of French coastline, with one last week reaching British shores with 83 people on board, the sources disclosed.

It came as the Home Office confirmed that almost 400 migrants crossed the Channel on Sunday, bringing the total to arrive so far this year to more than 9,000. Border Force dealt with 12 boats containing 378 people on one of the busiest days of the year so far.

It means 9,255 migrants have made the dangerous 21-mile journey this year – surpassing last year’s record total of 8,410. July has also seen a record-breaking 3,349 arrivals in 112 boats, beating June’s high of 2,179 in 92 boats.

On Monday, Border Force sources also revealed the ruthless tactics used by the gangs, which include assaulting men and using sexual violence and coercion against women if they refuse to get on board boats.

Some who arrive do not know they are in England and may never have wanted to come to the UK, according to the sources. One Syrian woman had paid to go to Canada but ended up in Britain on a small boat "because the facilitator gets paid when they arrive in the UK", said one source.

The smaller dinghies often deflate because of their poor state, putting families at risk of drowning, while children are crammed on board without life jackets. Sometimes the smugglers improvise with bicycle inner tubes or rubber rings bought from seaside shops.

Children and adults often arrive with burns on their skin because of having to fill up the ramshackle outboard engines multiple times as they make the crossing, said a source.

Border Force maintained that France was pulling its weight, with 8,000 migrants prevented from setting out to sea – treble last year’s figure at the same point – and interceptions of 2,700 on water.

However, the sources admitted France would not intercept or try to bring migrants on board their vessels if they refused or resisted, which was why they were escorted to British waters.

"We disagree in our interpretation of maritime law but we have to respect them as a sovereign nation. The French follow them to make sure they are safe," said one Border Force source. "It is a very dangerous environment and legally very complex. We are pushing every capability to see if it is possible to make interceptions at sea."