Fracking for shale gas is safe as long as operations are well-regulated and well-run, the main public health watchdog for England said on Thursday, after reviewing evidence from the U.S. on the controversial technology.

The study, from Public Health England, found that one of the biggest potential threats from hydraulic fracturing – the contamination of groundwater – was "likely to be caused by leakage through the vertical borehole" used for fracking.