Thomson pilot arrested at BHX
The brethalyser is for screening and the suspect has to be arrested if they fail, for a trip to the custody suite where the evidential test is done- you get to choose breath or blood. This will state the actual amount of alcohol and therefore is the evidence. If the officer has grounds to believe someone is drunk (alcohol on breath etc.), they can arrest on suspicion.
At the end of the day, it seems they had grounds to arrest but not to prosecute.
Plus- if you are sober, you won't have a problem.