Buying a knife and carrying it home is 100% legal, so there's nothing to "get away with" here.

Carrying a Santoku knife in public is only illegal if it's being carried without a "good reason" and carrying a newly purchased knife home is certainly a good reason.

The police have the power to stop and search people when they have "reasonable grounds" to suspect they're carrying a weapon; if the knife is clearly visible that's certainly reasonable grounds. So the search was not illegal.

A stop-and-search means being "detained" in the sense that you are not free to leave until the search is completed, but it's not an "arrest" that would appear on your arrest record. Perhaps there was a miscommunication about the distinction between being 'detained' and being 'arrested' ?

https://professional-troublemaker.com/2018/04/10/u-k-knife-c...

The article you linked does not support the claim that the UK police not liking someone's face is sufficient for them to be allowed to stop and search someone.

In fact, this goes directly against the PACE guidelines as described at https://www.college.police.uk/app/stop-and-search/fair

> A person’s physical appearance [...] cannot be used as the reason for stopping and searching them [...] unless there is information or intelligence giving a specific description of a person suspected of carrying an item for which there is a power to search.

Guidelines have never stopped authoritarian hell holes. They can just make shit up.