...and in British Birds Jan 2019

In July 2008 a Storm Petrel was caught bearing a Portuguese ring. One of our group, taking photographs and with time to look, noticed what he thought was a deeper 'thicker' bill than was usual for Hydrobates pelagicus pelagicus (nominate race). It was considered it might be a H.p. melitensis - the Mediterranean form of Storm Petrel. With due diligence and reference to others more knowledgeable in the field, plus the fact that this bird had been ringed by Rob Thomas of Cardiff University on 7 July 2007 at Ponta de Almadena, and had had samples taken for DNA, subsequent analysis was able to show it was pelagicus.
Adding melitensis to the British list was not to be, bad luck Stephen, but what this article did demonstrate was the difficulty in identification that remains for this species - even the deepest-billed birds may not (necessarily) be melitensis.