R (Venables and Thompson) v Home Secretary

R (Venables and Thompson) v Home Secretary [1997] UKHL 25 is a UK constitutional law case, concerning the exercise of independent judgement in judicial review. 
Facts.
Venables and Thompson claimed that the Home Secretary had unlawfully decided not to release them from prison, after they were convicted of murder as children. The Home Secretary took into account public petitions demanding the murderer be imprisoned for life. He refused to take account of their progress and development during detention. He increased the ‘tariff period’ from 10 to 15 years to delay release, and said they should be dealt with on the same basis as adult offenders, where mandatory life sentences were imposed.
Judgment.
The House of Lords held by 3 to 2, that the Home Secretary acted unlawfully by taking into account irrelevant considerations (a public petition) and failing to take into account relevant considerations (progress in detention).
Lord Steyn said the following of the Home Secretary.