Freedom of Information requests sent to 27 police forces around the UK have revealed the shocking extent of construction site thefts and their cost to the industry.

The collected data suggests that around 6,000 separate instances of thieves gaining entry to sites and illegally taking tools, materials and plant equipment were recorded between September 2012 and September 2013.

Data from the requests, submitted on behalf of secure storage unit supplier Mobile Mini, also uncovered the methods by which thieves are gaining access to supposedly secure sites.

In around 35% of cases, thieves used force such as breaking windows, cutting padlocks or compromising perimeter fences.

A further 5% were due to "legitimate access" in cases where the thieves either had a key, or turned up to a busy site and took equipment unnoticed.

Perhaps most worryingly, in 21% of cases sites were simply left unsecured, or were protected only by a fence that was easily scaled by intruders.

The findings could be invaluable to construction site managers who want to avoid becoming part of the statistics.

Commonly-stolen items included materials such as lead and copper piping, and power tools such as saws, drills and jackhammers.

Plant equipment, such as cement mixers, diggers and excavators, were also frequent targets of theft, suggesting that many criminals arrive equipped with trucks or vans to transport bulkier items. Opportunistic thieves also stole personal items, such as laptops and mobile phones left by staff.

Some regions emerged as clear hotspots of construction site crime. Devon & Cornwall suffered 372 separate incidents over the course of the year, police in Derbyshire recorded 241 cases and Thames Valley recorded 218.

"We were surprised to see that as many as one-fifth of thefts were due to a lack of on-site security and this should act as a wake-up call to many in the industry. The FOI data revealed that criminals are all too prepared to force their way into a secured site too," said Ron Halchishak, managing director at Mobile Mini. "Construction site managers should give careful consideration to their security arrangements and make life as difficult as possible for Britain's construction site thieves."

The full report can be viewed on the Mobile Mini website