I have never actually seen one in real life. I seem to recall it was a celebration loco as in Hornby brought it out to celebrate something. It was definately 1979. The strange thing is, they did not seem to come out with the 00 gauge version even though they could have as they had been made before.
I did notice that track for these large scale locos was sold for a few years after 1979.
They were quite expensive to buy which is why I never had one. (I remember when I was a child had to save for most of a year as I had around 10p or just over pocket money a week just to buy a 00 gauge loco which started at £2.50 for an 0-4-0 and was more like £6.50 for an 0-6-0 if I recall? Wagons were hovering around 99p to £1.50).
I remember my Dad looking at the leaflet, and then we saw the price on the seperate price list. He saw the price of the Rocket and told me "No".

(The price list was printed in black in 1979. It had brown print in 1978. The price list included as a seperate sheet in the catalogue, also had a few things that were not on the catalogue which at the time I did not know what they were (I do now as I later had a H&M3000). These were the H&M3000 and the H&M5000 which were train controllers made by a company called Hammat and Morgan, which in those days had close ties with Hornby, as H&M had used the same communication method in their H&M5000 as Hornby's Zero 1 had, and so they could both use the same loco decoders. 1979 was also the first time the Zero 1 was seen in the Hornby catalogue).
Budget modelling in 0-16.5...