Thankfully with such a short production run, there aren't many to choose from.
Faraday and
Franklin went to the RAF, so it wasn't those, and the other five remained with Imperial/BOAC when they moved to the old Whitchurch airfield in Bristol, from which they did the Lisbon runs. It would suggest it could be any of the five, although only 3 survived past 1940 (
Fingal and
Frobisher being detroyed in Oct/Dec 1940), and the rest had been scrapped or destroyed by the end of 1943.
On that basis,
Falcon, Fortuna and
Fiona are the survivors past 1940, and
Fortuna was lost in Ireland in July '43.
Falcon and
Fiona were scrapped a month later.
Shame really. Lovely looking aeroplane.