Decide firmly how one may go faster? (3,4,4,4)

I believe the answer is:

put ones foot down

This clue is a double definition.

'decide firmly' is the first definition.
(to put one's foot down is to assert a decision)

'how one may go faster?' is the second definition.
(using the accelerator in a car)

(Other definitions for put ones foot down that I've seen before include "Determined" , "accelerate" , "Take firm decision" , "Insist" , "Act firmly" .)

I've seen this clue in The Times.

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