From the Highway Code:
181
When turning right at crossroads where an oncoming vehicle is also turning right, there is a choice of two methods
turn right side to right side; keep the other vehicle on your right and turn behind it. This is generally the safer method as you have a clear view of any approaching traffic when completing your turn
left side to left side, turning in front of each other. This can block your view of oncoming vehicles, so take extra care. Cyclists and motorcyclists in particular may be hidden from your view. Road layout, markings or how the other vehicle is positioned can determine which course should be taken