The surviving gas works is now the Fakenham Museum of Gas and Local History, to give it its full title.
There is well produced video introduction that not only covers the history of gas making but also explains the process and what each bit of the site used to do.
Basically gas was made by distilling coal to give town gas, ammonia, coal tar and coke (all of which could be sold) along with some Hydrogen Sulphide.
The Museum includes a large collection of gas appliances as well as meters, lighting, calorimetery equipment, etc. There are also a couple of rooms dedicated to the local history of Fakenham.
All very interesting, if you like that kind of thing, which I do, even if most my friends seem to find the whole idea of a Museum of Gas rather amusing.
The plant closed in 1965 following the discovery of North Sea Gas. Nowadays its only connection with the modern gas supply system is a small Transco valve compound at the back of the site. These small compounds and are often the only markers of former gas works sites, apart from the few remaining gas holders.
As for their replacements, if you stand on the cliffs at Cromer on a sparklingly clear day, you can just make out three modern gas platforms on the horizon, and there is usually an LPG tanker in sight at any time of the day.