When chosing a Korean (or any other) restaurant you might want to consider their food hygiene rating. The score (0-5) can be found by searching www.scoresonthedoors.org.uk. Full reports are not made public but can, if you’re that curious, be obtained through a freedom of information request to the relevant council.
The idea of the ratings is for the public to make informed choices. Unsurprisingly only places with good scores tend to display the green sticker, the others presumably hoping you won’t ask. The website covers the whole UK and makes interesting reading.