I was taught that signals were not necessary on roundabouts. and if I wanted to give any signals they should be limited to indicating that I was leaving at the next exit.
The highway code quoted above says this, and the other signals it suggests is those required to get you into the correct lane going INTO the roundabout.
Roundabout discipline is crap in most cases, I have lost count of the number of people I have seen taking the shortest route across a roundabout and in so doing cutting across the lanes, and often the bumpers of other users. Ignoring the arrows on the approach indicating the correct lane for the exit you want is a common failing. Up in Inverness my nearest big town, it seems to be necessary to get in the outside lane if you're turning right at the next roundabout, at least 1½ miles before you get to said roundabout, without signalling of course, and usually at well below the relevant speed limit.
Giok