The identification of most of the machines and the scale of the haul indicates that police have found an important hub in the network for the first time, according to an insurance company involved, NFU Mutual.

A spokesman said the operation was a result of raised police awareness of a problem costing them and their subscribers £20m a year.

Ironically, EU funding is fuelling the trade, by creating enormous demand for farm machinery in the new member countries of Eastern Europe.

Typically, a tractor or quad bike is targeted, lifted on to a low-loader at midnight and is in a container aboard a ship the next morning, but until now police have found it hard to trace more than the odd item.

Russian and Ukrainian mafias are heavily involved, according to a police
source.

The Polish seizure was a result for the Serious and Organised Crime Unit of Kent Police, which secured the co-operation of Polish police.

Earlier this year, the Poles arrested two people in the Radom area who are being prosecuted.

Last month, more than 80 officers arrested five men in West Kent, Mid Kent and the Weald area. They were bailed pending further investigation.

This week, it was announced that six tractors, stolen from Kent, Hampshire, Sussex and Berkshire, had been returned to the UK.

An NFU Mutual spokesman, Terry Price, said farmers were in the front-line against organised thieving.

"Last year we saw a huge rise in metal thefts as commodity prices rose. Farmers have had irrigation pipes, gates, and even heavy pieces of machinery taken by metal thieves.

"This year's sharp rise in oil prices has led to a 30 per cent increase in red diesel thefts from farms.

"We're also dealing with widespread theft of central heating oil from homes in the countryside.

"Sometimes thieves will smash locks, damaging the tank in the process, or simply drill a hole in it to steal oil.

"Subsequent pollution can cost tens of thousands of pounds to clear up," he
said.