Highway code, Rule 186
186
Signals and position.
When taking the first exit to the left, unless signs or markings indicate otherwise
- signal left and approach in the left-hand lane
- keep to the left on the roundabout and continue signalling left to leave
When taking an exit to the right or going full circle, unless signs or markings indicate otherwise
- signal right and approach in the right-hand lane
- keep to the right on the roundabout until you need to change lanes to exit the roundabout
- signal left after you have passed the exit before the one you want
When taking any intermediate exit, unless signs or markings indicate otherwise
- select the appropriate lane on approach to the roundabout
- you should not normally need to signal on approach
- stay in this lane until you need to alter course to exit the roundabout
- signal left after you have passed the exit before the one you want
When there are more than three lanes at the entrance to a roundabout, use the most appropriate lane on approach and through it.
I have marked the rules regarding this cock up in bold
