QUOTE(earplugs @ Sep 24 2007, 10:29 AM)

Practise, and take them slowly at first. Getting the string stopped down in time before the bow crosses strings should help the flow. I think the hardest thing is slurred arpeggios on the descent. You need to practise being able to reach the 2nd, 3rd and possibly 4th finger (can't remember whether you need that in grade 3 arps) over one string while you are still playing it so you can stop the string down cleanly in time for the string crossing.
eg A major down from E (1st finger on D string) to C# (3rd finger on G) - you have to be able to play the C# with the finger nice and vertical without it touching the D string and stop it down fractionally before you cross otherwise you tend to get either an accidental 3rd finger G# on the D string or open G string as you cross with a slurred bow. Good left arm position with elbow coming round under the violin as you come down the strings should help with vertical fingers and getting the various stretches in tune too.
The scratchyness may just be that, because you are having to concentrate on the left hand the bow action is going wrong.
Hope that makes sense - easier to show than to put it into words.
that is good earplugs, all I was going to say was: plenty of 'slow' practice...I am finding that mine are getting better, they are still not perfect but certainly getting better and all I am doing is practicing them slowly, not stressing myself out or worrying that 'I'm not doing it well enough' and that so far seems to make the trick, but the advice that earplugs has given is far more constructive and helpful!