Per Lord Hoffmann in R v Secretary of State for the Home Department  UKHL 72, para 7:
It is not the case that the abolition of the death penalty must have been founded upon the premise that the life of every person has such inalienable value that its forfeiture cannot be justified on the ground of retributive punishment. A perfectly respectable case for the abolition of the death penalty can be constructed without subscribing to the view that the lives of Streicher, Eichmann, Saddam Hussein or Myra Hindley had such inalienable value that their executions could not be morally justified. Opposition to the death penalty may be based upon the more pragmatic grounds that it is irreversible when justice has miscarried, that there is little evidence that its deterrent effect is greater than that of other forms of punishment and that the ghastly ceremony of execution is degrading to the participants and the society on whose behalf it is performed. For people who hold such views, who must include many opposed to the death penalty, the parallels between the death penalty and life imprisonment without parole, to which Laws LJ draws attention, are the very reasons why they think that in some cases the latter sentence is appropriate. The preservation of a whole life sentence for the extreme cases which would previously have attracted the death penalty is for such people part of the price of agreeing to its abolition.