The current statute book contains much legislation that is now obsolete but still valid (particularly legislation that was passed in medieval times) or where acts of parliament have been superseded by new legislation without being abolished, leading to acts of parliament on the books which have clauses that are still vaild (because never actually repealed) or invalid (because repealed only in part).
An efficient statute book would see fewer, but up to date acts of parliament, with all old, outdated legislation (and the arcane rights contained therein) being cleared off the statute books. We should find the legislation affecting us contained in relatively few Acts of Parliament rather than spread across hundreds of acts of parliament, and trying to work out which bits are still valid and which bits aren't valid any more.
It is important that all legislation is written in plain English for two reasons. Firstly, if it can't be written in plain English, can we have confidence that the legislation is properly thought out at all? Secondly, to avoid poorly drafted legislation having to be amended by subsequent acts of parliament thereby eating up scarce parliamentary time.