I think you are referring to the situation when a judge recommends that someone serves a minimum time in jail - in which case it means that they will serve 21 years. I am not sure but I believe that the Home Secretary can let them out earlier, but it is unlikely to happen if the trial judge has specified a period.
I couldnt help but laugh at that one ineedahobby! do they have the internet for all to use in prison now?:} {if thats where you think i am,} someone i know was on a jury and thats what they got.