I'm late to this, so quickly, well done Bristol for at at least admitting that you have made an error. Just a couple of points to help you understand why.
You are driving a relatively long vehicle and overtaking on a left hand bend, which results in reduced visibility of oncoming traffic - you practically acknowledge this yourself. The cyclist is not static, probably moving at 15mph, so that by the time your back end clears him he will be somewhere near that post on the pavement. By that time you will have moved even closer to the pavement thinking you've completed the pass when in fact you haven't. This is exacerbated by the fact you're on a left hand bend.
There are plenty of documented deaths of cyclists by articulated lorries for this reason alone, the squeeze, and in some cases the driver was not even aware they had hit someone. I hope that helps.
PS The solution is to slow down behind the cyclist until you're round the bend and can see clearly enough to overtake leaving at least twice the distance between you and the cyclist. Ignore the impatient motorist behind you, this cyclist is someone's husband father etc.