Harry Roberts was sentenced to life imprisonment for each of the murders of three Police Officers - Police Constable Geoffrey Fox, Detective Constable David Wombwell and Sergeant Christopher Head. The trial judge (Wyn-Jones J) made a recommendation that he serve a minimum of 30 years imprisonment. The judge also expressed the opinion - "I think it likely that no Home Secretary regarding the enormity of your crime will ever think fit to show mercy by releasing you on licence."
In a decision condemned by the Police Dependants' Trust, the Parole Board for England and Wales has decided that Roberts may be released - The Independent 23rd October 2014.
In 1966, the release of a prisoner such as Roberts
was entirely a matter for executive decision and the responsible Minister was the Home Secretary. The involvement of a politician in this process came to be increasingly questioned and, in 2002, the House of Lords held that determination of how long a prisoner should serve did not meet the requirements of Article 6 of the European Convention on Human Rights - R v Secretary of State for the Home Department ex parte Anderson  UKHL 46. In essence, setting the period of minimum imprisonment was an aspect of sentencing and therefore a judicial and not political function. The Anderson case was preceded by V v United Kingdom (1999) 30 EHRR 121 where the European Court of Human Rights made it plain that the Home Secretary should not fix the tariff of a young
murderer ordered to be detained during Her Majesty's Pleasure.
The Parole Board dates from 1968. Today, it is established under section 239
of the Criminal Justice Act 2003. It operates as an Executive
Non-Departmental Public Body ('ENDPB'). The object of such
status is to enable the body to perform administrative activities free
from direct governmental control. An ENDPB must have a
sponsoring Department, which provides its funding and is concerned to
ensure that there is justification for the funding provided and that
this is used appropriately by the ENDPB. It was because of this that
the Court of Appeal criticised the lack of independence from the
executive of the Board - see R (Brooke) v Parole Board and Secretary of State for Justice  EWCA Civ 29
From July to November 2009, the government consulted on the future of the Parole Board and asked whether the Board should be transformed into a formal court
or become a tribunal. In October 2009, JUSTICE made a valuable contribution to the debate - Justice: A new parole system for England and Wales. However, the government consultation did not result in any change to the Board's status despite responses indicating that a change along one of those lines was
required - e.g. see Judiciary response.
The early release on licence provisions for those sentenced to life imprisonment are in the Crime (Sentences) Act 1997 section 28 (as amended). The Criminal Justice Act 2003 section 275 amended section 28 and the early release provisions will have come to apply to Roberts because of transitional provisions in Schedule 22 of the 2003 Act. It is an understatement to say that the legislation relating to early release is labyrinthine in complexity. Section 28(5) of the 1997 Act imposes a duty on the Secretary of State to release the prisoner as soon as he has served the minimum term aspect of his sentence and the board has directed his release. Section 28(6) prohibits the board from giving such a direction unless it is satisfied that it is no longer necessary for the protection of the public that the prisoner should be confined.
If released, an offender serving a life sentence will remain on licence
for the rest of their life. They may be recalled to prison at any time
if they are considered to be a risk to the public. They do not need to
have committed another offence in order to be recalled.
The Parole Board was the subject of the Supreme Court's decision in Osborn v Parole Board 
UKSC 61 which has required the Parole Board to reassess its practice
with regard to oral hearings which must now be held in a wider set of
circumstances than previously. On this see Ministry of Justice - Fair for the Future - Delivering on Osborn. One outcome of Osborn is that the Parole Board will now hold around 9000 oral hearings per year instead of the average of around 4500 previously - (Boardsheet August 2014). From 1st April 2014, an amendment to the Board Rules removed the need for a serving or retired judge to chair oral panel hearings for cases of prisoners serving a life sentence or a sentence during Her Majesty’s pleasure.
Osborn decision was interesting in that the court's decision was based
essentially on common law requirements rather than being based merely on
the European Convention on Human Rights and the Human Rights Act 1998.
This aspect of the case is discussed by Richard A. Edwards on the UK Human Rights blog 13th October 2013.
A clause in the Criminal Justice and Courts Bill is aimed at applying whole life terms to those who murder a Police Officer when in the course of his duty.
Legal Action Group - Parole Board Hearings - Law and Practice
Justice: The Parole system of England and Wales and also see Criminal Law and Justice 8th January 2010
Law and Lawyers - The Parole Board and victims
Public Law for Everyone - Osborn: The common law,the convention and the right to an oral hearing
UK Supreme Court blog - Comment - Osborn v Parole Board
UK Human Rights blog - Osborn v Parole Board
Additional Links - 25th October:
Guidance for Practitioners and Oral Hearing Guide
Parole Board Rules 2011 made by the Secretary of State - (see CJA 2003 s239)
Parole Board (Amendment) Rules 2014 (in force 1st April 2014) - amend the Parole Board Rules 2011 to remove the requirement for oral panels hearing the cases of prisoners serving a life sentence or a sentence during Her Majesty’s pleasure to include a sitting or retired judge and to have a sitting or retired judge acting as chair of the oral panel.