Riding on dual carriageways is not always easy. My own technique is to travel well out into the nearside carriageway so that you are well within the area that motorists scan long before they reach you. Most motor traffic will pull out into the offside (or next) lane. However you do need to look back at every vehicle as it approaches, though at night there is the additional visual cue of your shadow in the nearside headlight. Once in a while a motorist who has not looked ahead will come up behind; you then need to check that the vehicle has slowed and is indicating. If not (and this happens maybe once in 100 vehicles or so) you need to move smartly to the offside just before the overtaking vehicle reaches you so that the one foot they have allowed you becomes 5 feet. (I then have been known to have a word with them at the next lights and on one occasion, earlier this week, the elderly motorist concerned really did mend his ways and earn a wave of thanks when he then did a textbook pass; of course on other occasions they drive straight at me more determinedly than ever after I have challenged them). My experience is that HGV drivers almost always move early into the other lane; on the thankfully rare occasions they don't (happened yesterday) I have to move over and brake because they will cut in early.
This may not be for everyone and I can appreciate it cannot be done whilst time trialling but it works for me so I thought I would pass it on. Remember folks; never ride in the gutter.