I'm not sure of the origin of your premise, but I believe it's rather flawed; as Derek J. Oddy says in From Plain Fare to Fusion Food: British Diet from the 1890s to the 1990s: "Both wars brought about expediencies in the allocation of food but neither disrupted the long-term pattern of food consumption in Britain."

From my reply to a previous post about "traditional British food" and rationing, in which the poster was "thinking of foods like Baked Beanz and tinned tomatoes":

Rationing didn't have much of a long-term impact on British cuisine; "traditional British" dishes tend to either pre-date the 20th century (fish & chips, various pies, stews, hotpots, roasts, puddings etc.), with industrialisation being a driving factor in the 19th century, or post-date rationing (when "traditional" becomes more difficult to quantify, e.g. chicken tikka masala). Rationing restricted key elements of many dishes - meat, butter, cheese, fats, sugar - so wartime recipes focused on improvisation and substitution. Versions of popular dishes were hardly an improvement: toad-in-the-hole (sausages in batter, dating back to at least the 18th century in general concept) "... is not what it was. That lovely pork sausage in a yellow batter, shining with fat, has given place to a beef (save the mark) beast, flavourless and tough-skinned, in a heavy khaki batter made with milk powder". Bread was standardised as the National Loaf, a wholemeal recipe that made the most efficient use of flour but was not particularly appetising. New recipes focused on using unrationed foods (largely fresh fruit and vegetables) as far as possible and generally didn't last once rationing was lifted. King's College, London have the [Potato Pete recipe book] (http://www.kingscollections.org/exhibitions/archives/food/ww2/pete#Gallery) online featuring such delights as "Pink and Green Purée" (mashed potato with carrot and watercress and "a small piece of margarine or dripping if it can be spared"). [Lord Woolton Pie] (http://www.carrotmuseum.co.uk/photos/wooltonpie.jpg), named after the Minister of Food, was a vegetable pie topped with potato or wheatmeal pastry, "forced on somewhat reluctant tables" during the war and hardly a staple of post-rationing dinners; likewise [carrot flan] (https://www.iwm.org.uk/collections/item/object/205132636). The replacement of ice creams with a [carrot onna stick] (https://www.britishpathe.com/gallery/children-of-war/1) was another innovation rapidly forgotten post-war. I'm not sure I'd jump to tinned tomatoes being a traditional British food, except perhaps as part of a "full English" breakfast, but tinned foods were more of a luxury than a staple during the war. In 1942 a points system of rationing was introduced to cover "processed foods such as canned fish, meat, beans, and fruit; biscuits; rice, oats, and other cereal products; cheese and condensed milk; dried fruit and pulses; and certain preserves". These were items where supply fluctuated, so guaranteed rations by weight were impractical, but a points system meant that the rich were unable to corner the market where they were available, and points values could be adjusted to reflect supply. A person had 20 points to spend in a month; in 1942 tomatoes required 6 points for a medium tin, 9 points for a large tin; tinned beans in tomato sauce were 4 points, tinned beans in brine were 1 point.

A full English breakfast isn't a bad way of demonstrating the restrictions of rationing. Let's say you fry up four rashers of bacon, an egg, sausages, and fried bread, and serve it with tinned tomatoes, baked beans, and toast with plenty of butter. That single meal uses the best part of an entire week's ration for an adult (as shown in [this photo] (https://www.iwm.org.uk/collections/item/object/205195859) from the Imperial War Museum).

Rationing did have a democratising effect on food consumption, and was in some ways quite healthy with the focus on fresh vegetables, but was hardly conducive to appetising dishes that would outlast the restrictions.