Now, the history of British food is one of my areas. Prior to the ‘arrival’ of McDonalds and Kentucky Fried Chicken in 1974 and 1965, there was some limited consumption of hamburgers at Wimpy Bars/Grills, initially through Lyons’ Corner Houses and then as separate entities; they were served on plates with cutlery.
There were 35,000 fish and chip shops across the country in the 1930s, plenty of pie shops across London and in the postwar era, the rise of the greasy spoon/cafe (
https://thecritic.co.uk/hats-off-to-the-great-british-greasy-spoon/ ).
[ I will note that the article there does make a rather disparaging reference to the way with vegetables in wartime MoF British Restaurants, which isn’t necessarily accurate from a real food history point of view; the abuse of vegetables in cooking was more of a function of Mrs. Beaton.]
Let us divide restaurants and eating houses into three arbitrary categories:
1.) Upmarket
2.) Middle of the road
3.) Economy class
In the USA, there were more of Category 2.5 - 3 ‘neighbourhood restaurants’, on account of the different demography and history of various locales, but this wasn’t necessarily the case in Britain; there were some Italian places and a handful of Chinese restaurants in London and a few other cities, but food outside of the home was more the stuff of chophouses, inns and clubs in the English tradition.
Postwar, the ‘greasy spoon’ took on Category 3 quite well, and Category 1 was always there, but there was less of a middle category in the British practice. This would emerge later, as society changed, but after the period 1950-1975. Thus, when affluence improved by the 1960s (NHISG and all that), going out for a meal was a definite treat, be it in a newfangled Italian place, a Berni Inn, a Wimpy Bar or a McDonalds, in a manner different to the US.
Throw in a lack of car culture (a small factor, but a factor) and the cumulative impact of rationing, recovery and reaction to recovery and there was a very different background to British short order food.
The wider spread of Chinese, Indian and West Indian takeaways didn’t really kick in properly until the 1970s for the first two categories and much later for the third.
Without US restaurants and even without American foods such as the hamburger, we would still see British fast food, but in its own model/style.