The acceptable reasons for carrying a knife listed on that government article are:
Examples of good reasons to carry a knife or weapon in public can include:
- taking knives you use at work to and from work
- taking it to a gallery or museum to be exhibited
- if it’ll be used for theatre, film, television, historical reenactment or religious purposes, for example the kirpan some Sikhs carry
- if it’ll be used in a demonstration or to teach someone how to use it
None of those mention carrying an Opinel to cut up an apple, and are so obscure.
In addition, you have the Mayor of London saying there is never any reason to carry a knife [1]. I suspect if you're on a hike in the Yorkshire moors, you could be ok. On the tube in London, probably not. Either way, you are gambling on a policeman's discretion.
[1] https://mobile.twitter.com/mayoroflondon/status/982906526334...
The link posted says you can't carry some knives in public unless you have a good reason.
That's different from "Locking knives are illegal in public".