Are you just cherry picking the facts that may possibly be an explanation for the failure or are you ignoring the fact that he did actually fail a breath test (just as the union rep did in the radio interview)?
In any case, surely this is a one individual situation which should be dealt with by HR (or equiv of) and the individual (with union representation if desired). If he was unfairly dismissed and it went to arbitration then I am sure he could claim compensation. What has it got to do with anyone else and why is there a strike at all (effecting tens of thousands of commuters)?
Have you bothered to read anything about this case? The pertinent fact is not that he failed a breath test but why. He was not drunk and there appears to be no suggestion that he was. According to another poster, he was 1/10th of the drink drive limit. If that is the case, and the LU were aware of his type 2 diabetes, then why the sacking. If there is an issue, why destroy the urine sample? Common sense would dictate that you retain that until the issue is resolved.
With regard to action, what action can the union take then. He was dismissed, there was an internal appeal which upheld the decision (but let's be honest, that would have been carried out by LU management anyway). The LU won't go to tribunal which the Union have suggested so what should they do. Abandon their member to unemployment! There should be due process and it would appear from the face of it that LU are not interested in that. I am sure there are more facts that we are not aware of but I can only comment on what is in the public domain.
It seems you however, are only concerned with one line of the story, ie did he fail a breath test!
As an aside, a quick look at the RMT website would suggest that this isn't the only case where LU have destroyed evidence before an issue is resolved.
What I do agree on is that the Union rep didn't do himself any favours with his outburst.