I was going to say this is the 1920 Napier type 75 40/50 with “an all-weather cabriolet” body by Cunard, registration number XW 2454 (and still going strong without the white-wall tyres), but I then found a French website with this actual photograph describing it as a 1916 30/35, which is a bit odd as, according to Napier expert Ronald Barker, the company stopped all car production in 1914 and no more 30/35s were made thereafter. I am guessing the website may have taken the photograph from the Illustrated London News magazine which in 1917/18 ran a regular motoring column with articles on what motorists might expect to see when the war ended; so perhaps this is a prototype 40/50 with an old 30/35 engine, the actual 40/50 engine being delayed due to the chief engineer AJ Rowledge being busy working on the Napier Lion engine. But that's just a guess.
