In reply to captain paranoia:
> Agreed. On so many aspects of law. There has been a tendency to introduce laws banning things that are already illegal under existing legislation, if they chose to investigate and prosecute.
The problem is that if you are Parliament/the Government and find you have laws which are, for whatever reason, not being enforced, it is not always a matter of just telling people to enforce existing laws. So sometimes it is easier/more effective to just write better, more specific laws.
Sometimes things are illegal, but difficult to prove/prosecute successfully. Two possibly relevant examples:
Firstly, it was illegal to use a mobile phone while driving if that lead to the already illegal driving without due care and attention, but it was necessary to prove the driving error. Now that using a mobile while driving is illegal it is easier to prosecute.
Secondly, presumably driving while drunk was illegal before the limits came in (in the same way that it is illegal to cycle drunk but there is no limit), but it is presumably harder to prosecute someone who is only 'slightly' drunk, has character witnesses swearing they only had one/two pints etc... It is a lot easier to prosecute if you can just set a blood alcohol limit.
> 0.05 seems a reasonable level to choose. Zero is silly, and unworkable for many reasons.
Whether you agree with a zero limit or not is one thing, but it can't be unworkable as it works in some countries (albeit that zero probably means very-close-to-but-not-quite-zero in practical terms).