Before Covid burger and chips were average under £10, now the average is about £15. Probably along with many others, we stopped having lunch out on Saturdays. We now only go for a lunch out about once or twice a year.
But... food prices at the supermarket soared as well. This is nothing to do with eating out, it's eating in general! According to the web, food prices dropped slightly in 2020, increased slightly in 2021, increased 10.5% 2022, 19.3% 2023 and 7% 2024. if you spent £10 in 2019, food price inflation makes that £14.10 now. Throw in energy price increases (businesses go no energy assistance unlike domestic customers) using the appropriate values £10 on energy in 2020, is now £17.82....
That sounds like your £15 for a burger isn't unreasonable bearing in mind those issues.