Gangs are being paid as much as £13,500 to smuggle desperate migrants into the UK, the National Crime Agency (NCA) has revealed.

Criminal networks are also targeting quieter beaches like Kingsdown near Deal and ports across Kent and the south east coasts.

It has emerged traffickers are paid five-figure sums to arrange journeys for migrants by air, while others have spent £12,000 to travel from France in inflatable boats.

The UK's equivalent of the FBI, which is running the largest operation against organised immigration crime in Europe, says the cost varies hugely depending on whether the migrant wants a staged or "end to end" trip, how much they can afford and the level of risk perceived by smugglers.

The NCA's deputy director of border policing command, Tom Dowdall, said someone wishing to travel from Iraq to the UK, for example, could pay just under £4,000 to go by land through Turkey and Europe, while the price jumps to more than £13,500 for a journey by air.

Referring to the latter, Mr Dowdall said: "That's someone who has been able to access a good quality travel document in the first instance to be able to cross borders and to be able to fool airlines as well.

"There is a regularity to that."

One migrant found in a tanker at Dartford Crossing had travelled from Iran to Calais via Turkey, Hungary, Bulgaria, Greece, Austria, Switzerland and, once in France, Paris and Lille.

He had paid around 4,000 US dollars, or £2,800, to various "agents", with the journey to the UK costing an additional 1,000 euro, or £800.

On another occasion, six men found on a freight train near Folkestone reported that they had paid 500 euro, or £400 to get on at Calais, where they were sealed in containers.

The NCA's 90-officer taskforce - codenamed Project Invigor - has up to 60 open lines of inquiry into organised crime gangs at any one time.

Groups involved include those from the Middle East, China and various Eastern European countries, the agency said.

Smugglers find their "customers" through word of mouth recommendations, at transit hubs and via social media.