I have always wondered ...

[Dave Mann]

There isn't room on the quadrant for accelerator.

[AustinWood]

In the days when I traveled to and from Cambridge to Dundee for University I used the hand throttle on the A1. In the winter I could then put my feet on the gearbox for added warmth.

[Rick F]

I'm sure I remember reading somewhere - but cannot remeber where - that "Petrol" was actually a registered trade mark and as such Sir Herbert might have infringed something by using it. More importantly he might have had to pay someone!

[Mike Costigan]

Yes, petrol was the trade name for a nineteenth century cleaning product made by Carless, Capel & Leonard, which turned out to be most effective as a fuel in internal combustion engines! However, they failed to register it as a Trade Mark, so the word came into common usage for any brand of Motor Spirit.

[Peter Clayton]

Could have used  "+  CARB - " which might have made sense.   Used mine quite often as cruise setting when road conditions allowed.

[Mike Costigan]

I don't believe everything I read in Wikepedia, but this would suggest that gasolene was an English word before the Americans misspelt it 

   

[Charles Levien]

This is so very true — a couple of turns on the tick over screw plus a little choke makes starting with the handle a doddle.

[Rogerfrench]

When I was young some people used the word gas in a motoring context, like "stepping on the gas", "giving it the gas" etc., so I guess that even earlier it might not have been so much of an Americanism.
Motorcyclists had their own vocabulary, they spoke of "opening the taps", for example.

[Colin Morgan]

When I had driving lessons in the late '70s my instructor, who was about to retire, used say 'A bit of gas...'  So it was in UK parlance then. 

Can't think of another word that would have done the same job - 'Fuel', 'accelerator', 'right-foot' etc aren't as neat.

However, as mentioned, it seems likely 'Gas' as it appeared on Austin cars was influenced by American cars of the period?  The terms 'throttle lever' and 'gas lever' both seem to be used for instructions on driving the Ford Model T, for example.

[squeak]

Let's just say it stands for 'Go At Speed' if we wish to Trump the Americans.