Having finally cleared family duties I've had a few minutes to look into this and must say that I strongly agree with Mike Leven's views on this bird.
Roberson's material seems much more authoritative than the Indian field guides - tropicbirds are definitely NOT Pamela Rasmussen's first love and when you look at the text it is rather thin, simplistic and in places odd - talking for example of a 'short rounded' tail in Red-tailed, which is not borne out in the plates (having said that though I think her text still favours id as Red-tailed).
The bill of this bird in my view most closely resembles that of Red-tailed, and in no way resembles that of White-tailed - see Roberson's photos of actual specimens.
Moreover, Roberson states:
Upperwing patterns are diagnostic. At all ages (my emboldening), Red-tailed Tropicbird has virtually all-white remiges (primaries and secondaries) so they look essentially "white-winged" in the field. This works both on quite young birds and older individuals up through adults. This is easy! ...the outer primaries on some Red-tails have black shaft streaks, and some tertials have black centers, but these are very fine points. All Red-tails appear essentially white-winged in the field."
This bird was thickset in my view, resembling a booby when it first landed on the sea at great distance, then, after I'd called it as tropicbird, making me think I'd lost it and picked up an egret so white-winged was it.
I think it very closely resembles the photo at the end of Roberson's paper which he identifies as an immature Red-tailed of around 30 months, which one would apparently expect to assume full adult plumage in a further 12 months.
It's late now, and I just lost a first version of this, so I hope it makes a little sense - and of course we will need to refer these images to overseas experts, I think, to get a definitive id.
Mike Turnbull