Hi, this is mainly aimed at violinmac (I tried to reply to your post but couldn't!)

No, you are not required to do vibrato until grade 5, and even then, you don't have to be really fluent in it, it can take months and months to learn really well, and then years to be able to control it the way you really want to. Well done though for having a go at it in grade 4, one of my pupils did this too in her grade 4 exam and got the same response as you did in your exam, so i've leant now that it's not always a good thing to try it, as if you do it, you will be marked on it, if you don't, you won't! My advice to you for grade 5 would be to use vibrato only where you are really happy that it works, and works well...and don;t let it affect your intonation.

Good luck in your future exams, and well done for your Merit in grade 4