East Anglia's farmers have been warned to upgrade their vehicle security to stop criminal gangs stealing valuable satellite guidance systems during the coming harvest.

Rural insurer NFU Mutual said thieves could take advantage of the busy season during July and August to target expensive GPS (Global Positioning System) units from tractors and combine harvesters.

The company said these have been among the most frequently-stolen items from farms in recent years, because of their high value and portability.

Some farms have been hit by multiple losses of the £10,000 systems in thefts which can also cause costly disruption and delays at harvest time.

NFU Mutual saw the national cost of claims for GPS almost double in 2020 to £2.9m, although it says the figure has dropped in the last 18 months after a nationwide operation carried out by the National Vehicle Crime Intelligence Service (NaVCIS).

However, Norfolk farmers have been targeted in the past by GPS thieves who move around the country carrying out overnight raids. And NFU Mutual warned that thefts have been taking place in nearby counties of Bedfordshire, Cambridgeshire, Lincolnshire, Northamptonshire and Nottinghamshire in recent weeks.

Patrick Verrell, a senior NFU Mutual agent based in Swaffham, said: "We know that criminals are still trying to steal GPS kits and will take advantage of the coming harvest period when farmers are working long hours to get onto farms unseen and machinery is away from the farmstead.

"GPS is a vital tool on modern farms and thefts cause huge disruption as it can take days to source new equipment.

"With global food supplies under pressure, holding up harvest is the last thing farmers need. We are urging farmers to remove systems when they’re not in use and keep them securely."

Det Con Chris Piggott, agricultural vehicle crime co-ordinator at (NaVCIS), added: "These criminals are well organised and know what they are looking for - so it’s essential to remove GPS kit from tractors and combines when they’re not in use and store them securely.

"It’s also well worth using indelible ink to mark GPS cases and domes with your farm name and post code to make it less attractive to thieves - and to help police return recovered kit to its rightful owner.

"Many systems now have PIN security – and activating it makes it much harder for thieves to sell systems on.

“Some stolen GPS kits are offered for sale in the UK. One of the best things farmers can do to reduce this crime is to carefully check the provenance of any second-hand equipment offered for sale - including checking if it’s legitimate with the manufacturer.”

Farmers were also advised to keep photographs and serial numbers of their equipment, and report any suspicious activity to the police.