In basic terms... Southern Gas buy their supply a year ahead, in bulk, at todays prices from the energy makers. They then sell it onto us at an extortionate rate quoting investment in the system (pipes etc), shareholders to pay dividends, tax to the government and a very small profit...
They, and say Shell the people who get the stuff out of the ground, then make a huge profit and everyone is happy...
Apart from the end customer. Us.
Electricity is higher as we mostly ditched the cheapest option, nuclear, in favour of, and this is a doozy, burning gas to make electricity with a bit of wind and water power thrown in. This is then sold to the companies, then sold to you via the grid at an extortionate price.