share price27 Sep 2017 17:43
Stocks such as NG and the other Utes tend to be fairly robust (you always need their services). When interest rates are low people tend to buy because they give a fairly good yield of 4 to 6+% (NG to SSE for example). But when interest rates are threatening to rise (Mark Carney) bond yields increase. Bond yields are seen as safer than "risky" shares as so the money flows from the Utilities to bonds - hence the share price drops.
In the case of the NG and United Utes, we also have the likes of OFGEM/OFWAT sticking their oars in.
Then you have the threat of a re-nationalisation of the energy /water companies (yeah - right, does comrade corbyn know how much this would cost? - answer, no, but he was then advised - do the sums for yourself for the utilities but marked up at a premium!!).