Whatever the result of a referendum may be, I remain of the opinion that a transplanted population has no sef determination rights.
But what this discussion misses is that if the British government is really interested in self-determination, it would begin by working to relocate Chagoans deported from Diego Garcia, which would only require to deport a number of US military, who I think everybody would agree are not entitled to any kind of self determination. I also find really strange that some who advocate self-determination for the Kurds do not for the Palestinians (and I'm speaking for 1947, not for now), and only reluctantly granted it to the Scotts ; or that some support the creation of Israel, for which all historical grounds are fallacious, consider at the same time as ridiculous the possibility that France could claim the Channel Islands (which it is, but the case would certainly be much better). They have very accomodating views on self-determination and on historical legitimacy indeed.