The most severe sentence a court in England and Wales can impose is a sentence of imprisonment. The use of custodial sentences is, to some extent, limited by the provisions of section 152(2) of the Criminal Justice Act 2003 which states that: ‘The court must not pass a custodial sentence unless it is of the opinion that the offence, or the combination of the offence and one or more offences associated with it, was so serious that neither a fine alone nor a community sentence can be justified for the offence’. This provision serves as a reminder to sentencers that they should not be imposing a custodial sentence in circumstances where a non-custodial sentence may be an appropriate response to the offence.
There are different forms of custodial sentences. The vast majority of offenders who receive a custodial sentence will serve a determinate sentence with release from prison occurring automatically at the halfway stage of the sentence (with the second half of the sentence being served in the community on licence). Where a court considers an offender to be dangerous (and in other certain circumstances where a sentence is fixed by law) they may instead be sentenced to an extended sentence or a life sentence which have different release arrangements (see the separate sections on those sentences).
The Sentencing Council provides an explanation of determinate sentences with illustrations of how they are structured in practice: https://www.sentencingcouncil.org.uk/about-sentencing/types-of-sentence/determinate-prison-sentences/
Sentencing Council (2016) Imposition of Community and Custodial Sentences https://www.sentencingcouncil.org.uk/wp-content/uploads/Imposition-definitive-guideline-Web.pdf