Yeah Sunny Delight was definitely not around in the U.K. before the late 90s. My siblings went mad for it and it was disgusting!
I had taken the pp who posted about rationing to mean that the young adults of the 1970s, particularly the early 1970s, had grown up with menus and food that was shaped by rationing. My parents were working class young adults in the early 1970s and this was definitely true for them - they still talk about it. They had teeth ruined by National Dried Milk and sweetened rosehip syrup and blackcurrant concentrated juice (Ribena, for example, originated as a wartime solution to prevent scurvy in children during rationing). My paternal grandmother was still cooking with powdered egg and evaporated milk, and trying to give us spoonfuls of malt treacle well into the early 80s! The popularity of dried and packet foods in the 60s and 70s was partly influenced by habits derived from rationing (see also: cooking largely with margarine, drinking bouillon, Bovril and powdered milk drinks like Ovaltine, and so on).
Kids who were born in the late forties/early fifties definitely were impacted by the foods and cooking trends of the war years. My dad describes the whole of the Fifties as like living in black and white and still eating powdered mash and cabbage for most meals! British food was really really slow to improve and the 70s was when it first started to.
Someone mentioned Alpen upthread, which reminded me that late 70s food was really German and Swiss influenced! All that Black Forest gateau, Liebfraumilch, fondue, “health food”, bran, yoghurt and muesli! We had neighbours in the late 70s and early 80s who were “posh” and they had muesli and yoghurt, and were members of a tennis club, so they could be seen walking about the neighbourhood in tennis gear with the 70s headbands. They had an Alpine-style kitchen, a German car, and holidayed in West Germany. We were green with jealousy! West Germany was having a big economic revival at the time, and Britain was eyeing their success. It was the aspirational fashionable place to emulate, well before the French and Italian fashions of the 1980s really took off. In particular, it was notable that it looked like their lifestyle was healthier and wealthier, ironically much more so than Britain’s, partly because Britain took a long time economically to recover from the war.
By the late 80s it was super middle class and aspirational to go camping in France, and have French-style food for dinner parties, with Bordeaux, Perrier mineral water and Orangina for the kids. The nineties aspirational food culture was obsessed with Italy. But the 70s were all about West Germany!