Looking at the use of Macon ,Central France as a refuelling stop by Imperial's Empire boats I found this shot of Canopus with a Shell bowser nearby https://www.google.co.uk/imgres?imgurl= ... mrc&uact=8
Note that the no2 engine is missing with a dome shaped fairing in it's place . I conclude that it's Canopus' 3 engine ferry flight back to the UK after the June 1937 loss of an engine over the Med. Cambria accompanied it home apparently and there is also a photo of Cambria on the river at Macon