I wasn't sure if he would have got to sand casting in '77, but I do think that's how this was done.
I can't find my Glasshouse book to check there, but I have found Graham McLaren's little book; "Studio Glass 1960-2000", from which I can quote (p. 35-36)
"... Stourbridge College of Art ... stands out for its role in promoting kiln-forming techniques. The significance ... has largely been as a result of the teaching activities of Professor Keith Cummings...
Cummings' technical skill has been disseminated over the years via his seminal book "Techniques of Glass Forming" (1980) and through the students he has taught since 1968 at Stourbridge, many of whom are now leading practitioners. Of these, Brian Blanthorn, Tessa Clegg, David Reekie and Colin Reid are all outstanding in having extended kiln-forming processes in many ways."
There are images of his rather famous human figures, the earliest described dating to '87, just 10 years later than this bowl.
I was not sure how old Mr. Reekie is or how early he started working. This information suggests it was quite early.