"Drinking and Driving" joke

I heard the following last night-it's in the category
of "a friend of a normally reliable friend" and may be
apocryphal, but what the hell...
Following a really good party one night, the hosts
decided to leave the assorted bottles and dregs until the
next morning. As they staggered downstairs next day,
they found their young children finishing off all that
they could find, and looking the worse for wear.
Not knowing what to do, the father suggested taking them
out in the car for some fresh air. A traffic policeman,
seeing the car going round and round the block for no
reason, pulled him over and breathalysed him... and the
meter showed positive.
While matters were being sorted out, one of the children
asked the policeman if he could try the breathalyser...
and the meter again showed positive!
"Damn!" said the policeman, "another faulty meter!" He
then apologised to the driver for stopping him, and drove
off without another word...