Ian,
Let me just concentrate on the paradox then...
So we reach our paradox. I had concluded that I was just being given £10,000,000 to watch my favorite film of all time.
Translation: The self produced by Original Ian's brain concluded that it was just being given £10,000,000 to watch its favorite film of all time.
There should have been no danger to myself at all.
There was no danger to the self produced by Original Ian's brain but for the self produced by Duplicate Ian's brain, well, that's another story. It is going to die along with Duplicate Ian.
No, the only danger is to the self produced by Duplicate Ian's brain.
But this is clearly absurd!
It only seems so because you are using the term "myself" instead of "the self produced by Original Ian's brain" and "the self produced by Duplicate Ian's brain".
After all, how could it meaningfully differ from the situation where the same situation pertains yet no duplication takes place?
Because, in this situation, there is only one self so it is pretty straight forward: here is the self produced by Original Ian's brain and here it still is.
However when there is duplication there are two selves: the self produced by Original Ian's brain and the self produced by Duplicate Ian's brain. At the moment of duplication the brains and the selves are identical but not the same (afterall, there are two of them)
[where] no duplicate is created, there is absolute 100% certainty that I am the original Ian.
But who the hell are "you" anyway Ian?
Translation of your quoted sentence......
Where a duplicate is NOT created, there is absolute 100% certainty that the self produced by Original Ian's brain is the self produced by Original Ian's brain. (No arguments here

)
Where a duplicate IS created, there is still absolute 100% certainty that the self produced by Original Ian's brain is the self produced by Original Ian's brain. And now we also have a self produced by Duplicate Ian's brain which is...... the self produced by Duplicate Ian's brain. (Don't blame me Ian, it's your sentence I'm translating

)
It might be popinted out that at least the other Ian gets the £10,000,000. But this doesn't interest me anymore than anyone else I like who receives £10,000,000.
But who the hell are "you" Ian?
All we have is the self produced by Original Ian's brain and the self produced by Duplicate Ian's brain. Both of them feel as if they are "you". If, in one of the alternative scenarios, Duplicate Ian gets the money, "you" will get the money. But really that "you" is almost superfluous as I hope to illustrate below....
I honestly don't think there is anyway around this paradox apart from suggesting my own solution, namely that after duplication and before an Ian gets destroyed, in other words whilst there exist 2 Ians', I will simultaneously experience out of both of Ian's bodies. Otherwise materialism just generates an incoherency.
Yes, I can see why you think so. Your problem is "Where the hell is Ian?" If the self produced by Original Ian's brain is identical to the self produced by Duplicate Ian's brain and, if "you" are the self produced by Original Ian's brain, then you must also be the self produced by Duplicate Ian's brain. Therefore you say that "you" must be experiencing out of both bodies simultaneously. But can you not see that you are regarding the self ("you") as an entity that needs to take up residence in a brain rather than a process in a brain. In one way of looking at it, the "you" is superfluous because we already have two selves (that's okay because there are two brains) but where did this third self come from . In another way of looking at it, "you" are the self that the self produced by Original Ian's brain feels he is AND "you" are also the self that the self produced by Duplicate Ian's brain feels he is. But all we really mean is that what Original Ian and Duplicate Ian individually feel is identical.
regards,
BillyJoe
PS
You have shown us how what Original Ian and Duplicate Ian feel while watching "Groundhog Day" is identical. So, if Original Ian was executed and Duplicate Ian got the money wouldn't "you" be happy with that. I mean, "you" are still alive and have the money.
(Sorry, I have edited this a few times)