Calum, I live in the U.S., New York City. I had no idea either, even though I've been watching for probably that long. Time does fly! It is a wonderful little show--especially for history lovers. Just think, in 72 years the show will be an antique! I estimate its possible price at auction to be (insert dramatic pause here) = PRICELESS!
Anyone who tells a lie has not a pure heart, and cannot make a good soup. Ludwig Van Beethoven
The show in fact has been running since 1977. I can say this with absolute certainty as I'm sat watching the first programme in the new series and they're looking back at the first shows from 30 years ago.
According to Wikipedia a pilot show was made in 1977 but the series really started in 1979. The BBC website refers to it as 1979, too.