The Highway Code applies to England, Scotland and Wales and is essential reading for everyone who drives.
Box junctions. These have criss-cross yellow lines painted on the road.
You MUST NOT enter the box until your exit road or lane is clear. However, you may enter the box and wait when you want to turn right, and are only stopped from doing so by oncoming traffic, or by other vehicles waiting to turn right.
At signalled roundabouts you MUST NOT enter the box unless you can cross over it completely without stopping.