The rising price of lamb is causing a spate of crimes — in the latest, a 1,500-strong flock was spirited away in Lincolnshire

They were the sheep that passed in the night. A 1,500-strong flock has been spirited away in the dark from fields in Lincolnshire in what is believed to be the biggest case of rustling in Britain in modern times.

The theft at Stenigot near Louth, which fleeced the farmer of an estimated £100,000, is the latest in a spate of crimes driven by the rising price of lamb.

The level of organisation needed to carry out last weekend’s operation has surprised insurers and police.

“It would have involved sheepdogs, up to five articulated lorries and three men with each truck,” said a spokesman for NFU Mutual, the insurance company. “There would have been a lot of whistling and calling to the dogs. It is a remarkable achievement.”

He added that even in broad daylight experienced shepherds would find it hard to move so many animals in less than three hours.

The company estimates the cost of sheep rustling has risen more than fivefold in the past year. It says thefts of 100 to 200 animals have now become common and has received 142 claims for rustling in the first six months of this year, compared with 156 for the whole of 2010.

There is money to be made from lamb. The cost of 1kg (2.2lb) of British chops has gone up almost 40% in three years, from an average of 1,039p in July 2008 to 1,424p in July this year.

The price rises date originally from the foot-and-mouth crisis of 2001 when the number of sheep decreased sharply. More recently, falling farm profits and two harsh winters, leading to poor pastures, have reduced numbers further, while the weak pound has encouraged farmers to sell them abroad.

Recent thefts, reminiscent of those encountered by Wallace and Gromit in A Close Shave, include 300 sheep taken from a farm near Hungerford, Berkshire, 200 from a flock on Dartmoor in Devon and a similar number from Cockburnspath, Berwickshire — as well as 271 at Ramsbottom, Lancashire.

Previously, the biggest livestock theft in recent years was in 2009 when 500 piglets were taken from a farm in Staffordshire. Ducks and bees have also been singled out.

Sheep rustling has attracted skilled criminals in the past. The 18th-century highwayman Dick Turpin began his career stealing them for his butcher’s shop in Essex.

Modern thieves, as well as being well organised with fleets of transporters and a network of helpers to process the animals, are adept at pulling the wool over the eyes of police and other investigators.

Farmers are required to tag and document each animal, suggesting thieves may be falsifying records or be in league with slaughterhouses willing to kill the animals illicitly. Some may also end up in the fields of dishonest farmers who “launder” their identities.

Organised rural crime is a growing menace, although it is more common with machinery than livestock. “We’ve just recovered a Land Rover that was stolen from a farmer in Warwickshire as he went to unlock a gate,” said Chris Ruff, a detective with the vehicle crime intelligence service of the Association of Chief Police Officers. “It ended up in South Africa.” The service also recovered nine tractors from Poland.

There were 507,906 crimes in the countryside between January and June, compared with 195,907 over the previous six months, according to research commissioned by NFU Mutual.

It believes the spike in rural crime is in part driven by rising prices for sheep meat and materials such as scrap metals and diesel fuel — and peaks each April.