Stuart. I don't know whether Lutonman was also involved with the manufacture of gas, I'll leave that to him. But a consequence of the manufacture was that there was a lot of coke left after the gas had been extracted. This was used commercially & industrially for heating systems; Schools, Hospitals, factories, etc., although very large installations using steam still used coal( anthracite or large "steam coal"). Most large towns had a gas works, with the obligatory gasometer, or 2 or 3, to store the gas. These, as you said, could increase in volume by moving the inner tanks up (usually 3 in total), with a water seal within a " gutter"- about 10" wide & deep- between them. The system worked quite well as the gas was not at a great pressure & 12" mains were standard in towns, going back many years to the gas lit streets & homes. Trouble occurred when "natural" gas was discovered in the N.Sea & more so, in the Middle East. It was much cheaper in comparison, so became a must have & didn't smell BUT worked at a much higher pressure. Because of this increased pressure, which was reduced somewhat for domestic/ commercial use, the gas could be compressed & stored in H.P. pipes, doing away with the gasometers. And the gas works of course. So no more coke. But this was replaced in commercial/industrial heating by this new, cheap gas. So there was a nationwide change over of heating boilers from coke to gas, quite a big programme in which I was very much involved in the mid 70's. A few years later came the " clean air act", so coal became a no no & was replaced domestically with "smokeless fuel"( bricquets, etc.) & industrially, larger hospitals etc., by heavy oil or gas. As mentioned, this natural gas was at a higher pressure than " towns" gas & caused problems in places by leaking, with the consequential explosions! My brother on law was an engineer with a firm who did gas & fuel pipelines across the country( my sister met him when he was an x-ray welder at the IoGrain oil refinery). One job,they were tasked with replacing the mains in Cambridge & found that in places the original pipe had rusted way & the gas was held in place by the solid clay surrounding it! There must have been hundreds similar! Someone asked about the areas occupied by gasometers- what happened when they were no longer needed. It was a very precarious situation for the ground beneath was highly toxic with " heavy metals" etc. The only way to use it safely was to excavate the whole are to a depth of 12ft.! Occasionally, like the one in Carlisle which my B in Law( now working for Brit. Gas) was about to take down, suddenly had a court order prohibiting the demolition as it was of " historic significance"! I've tried to precis this but any more questions, please ask &, hopefully, I will be able to answer.