In England, does a 24 years sentence mean 24 years in prison?

If the sentence is for 12 months or more

For prison sentences of 12 months or more the person spends the first half of the sentence in prison and the second half in the community ‘on licence’.

If they break any licence conditions - eg they commit another crime - they could go back to prison.

If the sentence is under 12 months

For prison sentences under 12 months, the person’s normally released automatically halfway through.


Life sentences

If a person’s found guilty of murder, a court must give them a life sentence.

A court may choose to give a life sentence for serious offences like:

rape
armed robbery

A life sentence lasts for the rest of a person’s life – if they’re released
from prison and commit another crime they can be sent back to prison at any time.

Whole life term
A whole life term means there’s no minimum term set by the judge, and the person’s
never considered for release.

https://www.gov.uk/types-of-prison-sentence/determinate-prison-sentences-fixed-length-of-time

nothing to do with manslaughter

I think the judge must have sentenced him to a minimum of 24 years, after that eligible for parole

its a technicality really because as you say a life sentence doesn't really mean that in almost all cases

"In England and Wales, the average life sentence prisoner serves around 15 years before being paroled, although those convicted of exceptionally grave crimes remain behind bars for considerably longer; Ian Huntley was given a minimum term of 40 years."