Current measure is a mere pig-headed intervention (6)
I believe the answer is:
ampere
'current measure' is the definition.
(measure of electrical current)
'a mere pig-headed intervention' is the wordplay.
'a' becomes 'amp' (A is the symbol for the amp or ampere).
'mere pig-headed intervention' becomes 'ere' (I can't justify this - if you can you should give a lot more credence to this answer).
'amp'+'ere'='AMPERE'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for ampere that I've seen before include "Unit of currency" , "Solenoid inventor" , "Unit measured by 17 across" , "Basic SI unit of electric current" , "Current measure" .)