Despite recent price rises, the percentage of income spent on food is a fraction of what it was even 20-30 years ago, and is much less than many other countries.
There's also a huge amount of 'luxury' food consumption that can be cut back on if necessary to ensure that people get enough to eat such as drinks other than water and tea/instant coffee, ready meals, takeaways, imported fruit and vegetables, meat more than once or twice a week, bought lunches, meals out, many processed foods, snacks, cakes, sweets, crisps etc etc, the list goes on.
Of course some people don't have enough money for food, but for the majority, it's going to take more than a few pence of price rises here and there for them to not be able to afford enough to eat, even if they don't get to eat what they're used to eating.
Vegetarian is cheaper than meat eating, when comparing like with like. The lasagne example above - the amount of lasagne made by a pepper, aubergine, courgette and mushrooms is going to be quite a bit more than half a pound of mince, so of course a big pile of veg will be more than a small pack of mince.