… shown by them getting pissed in Somerset, possibly (12)

I believe the answer is:

speedometers

'shown by them' is the definition.
I can't judge whether this defines the answer.

'pissed in somerset possibly' is the wordplay.
'pissed' becomes 'peed' ('pee' can be a synonym of 'piss').
'in' indicates putting letters inside.
'possibly' is an anagram indicator.
'somerset' anagrammed gives 'someters'.
'peed' put within 'someters' is 'SPEEDOMETERS'.

'getting' is the link.

(Another definition for speedometers that I've seen is " Indicators of velocity".)

I've seen this clue in The Guardian.

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