Murder: a whole spectrum of conduct". In 2004, the Law Commission described the law as a "mess" and, in 2006, published their report - Law Com 304 Murder, Manslaughter and Infanticide. The Commission recommended fundamental reform and proposed a new Act of Parliament to create a 3 tier structure for general homicide offences. The government (as is often the case) cherry-picked the report and implemented reforms to the law relating to "partial defences" to murder - see Coroners and Justice Act 2009 Part 2 Chapter 1.
It now seems that the new government is attracted to the idea of reforming the law of homicide along the somewhat complex lines suggested by the Law Commission: First degree murder; Second Degree Murder and Manslaughter. See Telegraph 13th July.
It is worth noting that the Law Commission's report was in 2006 and there is therefore a case for reform even if not exactly on the lines suggested by the Commission. We know from Kenneth Clarke's speech (looked at here) that the government wishes to reduce the prison population. The removal of the mandatory life sentence for some murders - (i.e. those classed as 2nd Degree) - will assist with that aim. It is perhaps unfortunate that the aim of reducing the numbers in prison is likely to be seen as the main "driver" behind government's conversion to reforms suggested some time ago.