That is the problem though. You are supposed to tell them every single thing that concerns the application. You are building trust with the UK authorities, and by skipping on certain information that they later discover you missed out is not the way of building trust.
As far as they are concerned, they were mislead once, so where else are you doing it? Hence the hiccup with the caterer. They cannot contact them for one reason or another, so why should they believe you when you've already tried one over on them previosuly?
Look at it this way, you are interviewing applicants for the job of looking after a dying family member 24/7 and the one you were going to employ you discover missed some vital information out of the application. Would you still trust them enough to look after said dying family member?