Prison sentences: How do judges decide them?

Changes are in the pipeline for the sentencing of sex offenders. But what principles govern how long a criminal is jailed for? During the reign of George I a person could be executed for posing as a gypsy. Attempted murder was classed as a "misdemeanour" until 1803 whereas forgery was a hanging offence. The seriousness with which particular crimes are viewed shifts according to the mores of the day. Who decides on a criminal's fate has also changed. In the past capital punishment might be down to the whim of kings and queens, Parliament or the discretion of judges. Today there is a body that hands down sentencing guidelines to judges. The Sentencing Council, which covers England and Wales, has just announced a consultation into how sex crimes are punished.