Thanks, loo,
I've sent an email to St. Edmund's - let's see what happens!
It also occurred to me that an explanation for the registration of two births, that actually took place 18 months apart, on the same day could be that the British Consulate was either understaffed, or didn't take their civil registration duties very seriously, and some lowly clerk was eventually obliged to sit down and spend a day dealing with a large backlog of registrations.
By the way, in case anyone is scrutinizing this thread, the births were 18 months apart, not 2 years as implied in an earlier message, where I was guilty of a typo!
Cheers
Tim