At present politians feel they need to be seen to be 'doing something' so each session must have new laws to debate and enact.
This tends to encourage the making of law. If all laws became defunt after a set time, then each parliament would need to spend more time debating and re-enacting the necessary ones in, updating them, and therefore have less time available to expand the number and breadth of the law.
Legislators will be best to decide what the period for this sunset clasue should be – it could vary, but the net effect will be to clean up all our law over time.
Why does this idea matter?
1. If laws are automatically removed after a set time, polititians will have to spend more time updating the good ones and have less time to dream up unecessry ones.
2. The Law can never accommodate all situations, for example it is not the act of using a mobile phone while driving, but the act of driving without due care and attention (because you are on the phone) that is the crime. The law was introduced to deal with a specific (hopefully temporary problem.) There are many other actions not covered by specific laws, having and argument, being distracted by the kids, looking at a pretty girl, eating a sandwich etc that are just as dangerous. The law was brought in to deal with a specific (probabaly temporary issue) but will remain until repealed.
Far better to have fewer broader laws ie 'driving without due care'. Frame th law to describe the intent do not attempt to specify all circumstances. Let the Jury decide if a man using a phone in a stationary queue is breaking the intent of the law, or a mother should have pulled over to talk to the kids. Less time to legislate will mean fewer broader laws and a more flexible society.
The UK has a tradtion of common law that was based on the 'reasonable man' which allowed the exercise of 'fair and sensible judgement' in a rather flexible but admittedly often messy way. Coping with that uncertainty creates innovation and debate. It can be abused, but it is false to believe that any amount of regulation will cope will all circumstances or bring justice.