Plant theft from building sites is costing the construction industry £800million a year according to a study by insurer Allianz Cornhill. About £70million worth of plant - especially JCB diggers and compressors - are stolen annually. But the real cost to the industry is far higher when the cost of hiring replacements, loss of business and higher insurance premiums are taken into account. Although the cost of plant has risen 5 - 10% over the past five years, premiums have jumped 40% and are set to rise further. Plant theft also tends to rise when construction activity slows.