Sure is. Went there on an O level Geology field trip in about '87. As per the above video the guide explained that the main spikes in demand were during the adverts when Coronation Street was on and at half time on the (then very occasional) televised football matches.
Dinorwig was built in the 70s, lot of the same principles https://en.m.wikipedia.org/wiki/Dinorwig_Power_Station
Edit, just seen schmunk is already on the case :)