More difficult than it appears! It presumably is the WG Tuck/Philip Rampon Humber, later known as the Martin-Arab, but it doesn't have the original engine (exhaust on the wrong side), which blew up spectacularly in 1920; not does it appear to have a big V8 Sunbeam Arab engine, which presumably would have had a pipe on either side. Bill Boddy suggested that it was briefly fitted with a third engine originally intended for the 1913 GP Vauxhall but never used (it didn't last long, blowing up in even more spectacular fashion in 1921).