A gang who stole £700,000 worth of heavy plant machinery which was shipped out to Eastern Europe were jailed for more than 20 years today.

Brothers Stacy and Lee Dunn, their father Lee Dunn senior and associate Richard Scales were involved in the theft of JCBs from construction sites all over Hertfordshire.

Prosecutor Simon Wilshire told St Albans crown court said the case concerned the "systematic theft" of heavy plant machinery with a view to exporting it to Eastern Europe. Police identified 17 actual thefts and two attempted thefts, but he said: "The crown consider these 19 instances to be the tip of the iceberg."

More than £700,000 of plant was taken with £309,000 recovered. One example of theft was just before ten past five on the morning of February 28 last year a JCB was stolen from a construction site in Bushey.

Mr Wilshire said the thieves failed to locate a tracking device fitted to it and police were able to establish that around 30 minutes later it was inside a barn.

The police continued to monitor the JCB in the days that followed and then on March 5 last year it became apparent the JCB was on board a Polish articulated lorry travelling on the M25 bound for Dover.

Three locations were used by the thieves to store heavy plant and machinery and change identifying features. When a stolen vehicle was recovered from the Potton End storage site, police found a cigarette butt there, which was found to contain the DNA of Lee Mark Dunn. A contact phone number given by a man when booking a storage facility at Mentmore Boat Yard could be attributed to Lee Paul Dunn. Keys to open padlocks at the site were later found by police in Lee Paul Dunn's VW car.

CCTV cameras also captured on film Stacy Dunn loading a stolen JCB onto a low loader at Fir Tree Farm.

Stacy Dunn, 36, of Cecil Street, Watford was sentenced to 5 years 9 months, his brother Lee Paul Dunn, 32, of Matlock Cresent, Watford, received 5 and a half years, their father Lee Mark Dunn of High Street, Bedmond, Abbots Langley also received 5 and a half years. They had all pleaded not guilty to conspiring to steal between January 1 2011 and March 7 last year, but were convicted by a jury.

Richard Scales, 48, of Alder Close, Park Street, St Albans pleaded guilty to conspiracy to steal and possessing 4.5 grams of cocaine which were found in 9 wraps at his home. He was jailed for a total of 4 years 4 months.

Lucy Dunn, 32, who is Lee's wife from Matlock Crescent, South Oxhey, who pleaded not guilty to two offences of transferring criminal property by paying £2,500 into her Barclays Bank account and and later withdrawing the sum of £6,000 from the account. She was found not guilty. Her husband was cleared of transferring criminal property by paying £3,700 into his wife's account For Stacy Dunn, Michael Gomulka said the thefts had been carried out late at night when nobody was about. He said there was no evidence that he had played a leading role.

Andel Singh, for Lee Dunn senior, said he was the sole carer for his wife who is on disability living allowance.

Mr Singh, who also represented Scales, asked for credit for his guilty plea and said he was only involved towards the end of the conspiracy.

For Lee Dunn junior Jonathan Mann said no violence or criminal damage had been used in the thefts.

Judge Stephen Warner said: "This was a sophisticated conspiracy to steal plant and machinery from building sites in Hertfordshire. It was over a period of 14 months and required a significant amount of planning and organisation to arrange to steal the plant, transport it to storage, to disguise it and move it out.

"The items taken were of high value. It was a lucrative trade - a commercial enterprise on a significant scale which had a serious impact on construction projects and the community."

At the end of the sentencing the judge praised the officers in the case for their investigation.