I'm not sure when the distribution networks were separated off for regulation as a distinct entity, but it must have been before 1996. Coal gas production and storage was I think always local, and the national transmission network only arrived with natural gas. I found an NGN report saying they had a regulatory target to demolish 23 of their 47 remaining holders by 2020
In the South West, and I assume elsewhere, there was an intermediate phase. Coal based town gas works were closed and replaced by oil based plants at Avonmouth (Seabank) and Plymouth (Breakwater) with a regional gas transmission system. Seabamk is now a
CCGT▸ power station.