London Tonight has discovered that a high security fence is being built around a gas plant in Hertfordshire. The plant is tucked away in woods.
It's believed the site supplies gas to north London and Stratford - including the Olympic park. Around one hundred workers are erecting a fence around the site.
Work will continue there for the next five months.
The National Grid said in a statement: "We carry out robust security in conjunction with the Government and LOCOG [The London 2012 Organising Committee]."