Compared to the rest of the world, the average UK citizen spends less on food as a percentage of their total income than nearly every other country. This is a fact, not a conjecture or debating point.
Source: https://ourworldindata.org/grapher/share-of-consumer-expenditure-spent-on-food?mapSelect=~GBR
Industrialisation and retail competition have driven food prices down in the UK. But other costs have risen (housing) or have been introduced and are now deemed essential (internet, media, electronic goods) and so on, so:
"...the proportion of total expenditure on housing has doubled during the last 60 years, from 9% to 18%. On the other hand, the proportion of total spending that went on food has halved (33% to 16%), as has the proportion on clothing (10% to 5%)"
Source: ONS, https://blog.ons.gov.uk/2018/01/18/celebrating-60-years-of-family-spending/
Objectively, we do have a low-cost food economy, because we are proportionally richer than the rest of the world, and so we spend proportionally less on food per capita.
This obviously doesn't mean that everyone in the UK can afford food, but it does mean that on average over 90% of expenditure is on non-food items (housing, cars, etc.), so most people can afford to eat - and eat well - if they choose to.
Subjectively, of course, some people do feel squeezed. But, any MN follower will know that some people feel 'squeezed' on 150K p.a., when others are coping just fine on 36K p.a. (the median household income in the UK).
So, it's a subjective feeling which may or may not relate to real, material circumstances, alongside personal expectations and perhaps an assumption that you will do better than your parents - no longer true for the middle classes.
So, yes, food is relatively speaking less expensive than it was in the past, as a proportion of household income. But, subjectively, for some, it just feels more expensive, as do many other things.