'Adventurous Empires' by Phillip E. Sims, published by Airlife ISBN1 84037 130 7, confirms the post by Norman Atkinson that Golden Horn was a Short S26 'G-class' flying boat, first flight 24 February 1940, RAF X8273 July 1940 and BOAC December 1941, plus on p204 gives an account of the loss of Golden Horn.
In summary, on 9 January 1941 Capt Lock took Golden Horn on an air test following an engine change. While respected by the staff at Lisbon, he apparently breached orders from London and those on board included a number of unauthorised passengers, including customs officers, loaders and wives. It would also appear that he had his own ideas with regard to cooling gill and oil-cooler settings, and it may be that during this flight he put these theories to the test. What is known is that Golden Horn experienced an engine fire that, due to the lack of extinguishers in the Hercules engines, became uncontained, affecting the tail surfaces and, due to the nature of flow around the aircraft, filling the cockpit with thick smoke. Capt Lock was unable to see out during the landing and crashed into the Tagus, with only two survivors. The exact number of those perished is, due to the number of unauthorized passengers, unknown but may be at least a dozen.