I think I would have been in the RH lane too.
If I need to cycle in the RH lane on a dual carriage way I do three things:
1. cycle like a demented fat man…if car drivers can see you are trying to go fast they understand that you know you are "in the way" and are trying to get out of the way and back to the left side ASAP.
2. If I need to be in the RH lane for more than 50-100m then I try to keep to the RH side of the RH lane, this gives drivers the chance to undertake easily if the LH lane is not busy ( I tend to do this only on one roundabout in Leeds …Skyliner roundabout coming from Sainsburys, turning towards Crossgates)
3. Be confident and exagerate your hand gestures. Let drivers know that you know what you are doing.
….oh bugger…number 4: try and find a friendly driver to use as a sheild. If you are in the LH lane and have plenty of time, stick you right arm out and keep an eye out over your shoulder. Once a friendly driver flashes or hangs back to let you move lanes use him/her to sheild you while you repeat the exercise to get into RH lane. Any driver that has made a choice to give way to a cyclist is on your side and will not mind being "held up" for a couple of hundred yards.