I can tell you precisely why you probably didn't see him. The same reasons that most 'looked but failed to see' accidents occur, which you pretty much suggest in not quite so many words.
These are to do with effective observation. Generally people combine, in varying measure, making decisions too quickly, and failing to double check their decision making.
How often, for example, do you see a car approach a give way junction fast, throw a quick glance right and pull out left, causing either approaching traffic to brake, or then having to brake heavily for something they should have seen to their left before emerging. It doesn't take much for this sort of behaviour to degenerate into a more serious incident.
Let's have a look at some of the clues:
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the mini roundabout width is incredibly small and only perhaps three pedals needed to clear it
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The smaller the roundabout, the quicker danger will reach you, so the more careful you have to be with your observations to stay safe. My alarm bells are ringing.
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I understand traffic to the right has right of way but when a car to my right has stopped to give way to me it necessitates that I should have entered the round about
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No it really doesn't necessitate anything of the sort. It means that following an appropriate observation you might decide to proceed onto the roundabout if you are sure there are no other dangers and you are sure of the other driver's intentions.
However, what usually happens when someone lets another person out is that the beneficiary feels the need to rush and get on with it (which you are kind of hinting at in how you have written it). Which results in mistakes being made in observation. It is why learner drivers are taught never to flash or wave another road user to do something.
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so proceeded to enter the round about. I then hear a thud and a cyclist has collided with my rhs near the mini round about
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This says very strongly to me that once you have made the decision to move forward you have stopped looking right - if you hadn't you would have seen him at least even if you couldn't avoid the collision. Check, and double check before committing over the give way lines, then check again even as you are entering the roundabout/junction. Too often people stop looking too early.
Learner drivers are often taught at give way lines to Look, Assess, Decide and Act. How long do you think it takes to go through these steps? Trust me as someone who does this stuff day in and day out, most drivers approach too fast and don't take enough time making decisions. Fast approaches and quick observations feel like good driving until the day they let you down...