Ah, I see- thanks for that, Henry, I didn't think to check the 1952 edition! I couldn't find Elizabeth A. M. d'Abreu in U.K. birth records (nor in fact could I find anything at all, really), and from Richard's information it doesn't sound like she's in that family's pedigree (although I'll have a look just in case), so I might have to put a pin in this one!
Interestingly, Francis Arthur Philip d'Abreu's entry (not including his third forename, but the details- father, year of birth, brother- confirm it's him) in the Lives of the Fellows on the Royal College of Surgeons website states him to have been one of twelve children, not reflected in the 1952 pedigree; this perhaps opens the field. A quick look at U.K. birth and census records would seem to support the 1952 pedigree, though... confusing! At any rate, a bit of digging shows the Abreu (and variants) surname to be less rare than I had initially thought, so of course there very well might be no relationship despite what is otherwise something of a coincidence in two related Tritton marriages.