what is the definitive procedure for drink drive testing?

[bryan35]

out of curiosity really,

is it.........
road side stop, hand held breath test machine.
if it shows red, then off to station and big posh breath test machine.
20 minute wait, no drinks aloud, 2 tests, discard the highest.
if <35mg/100ml then released without charge,
if >35 but <40 released but with flea in ear,
if 40 - 50 option for blood test,
if 50+ it's all over.