I can remember the "give up when they go over a pound" days very clearly and I'm pretty sure that was 1983/84 so in 1977 they'd have been considerably less. Doesn't answer your question, but it's a step on the way :)
I can remember being able to buy 10 sovereign or 10 number 10 for 9 and half pence, for half pence you could buy a book of matches. thats what my 10pence lunch money for school, went on. that was the 70s