Then let's just not release?
You can't just ramp sentences endlessly upwards without introducing unintended consequences. Aside from the question of cost, staffing, facilities etc, you introduce an element of 'what the hell' thinking into the minds of criminals.
We already know that tougher sentences, even capital punishment, do nothing to act as a deterrent, so while, on the face of it, longer sentences might go some way to appeasing public feeling (which I have my doubts about because some people will never be satisfied regardless), you can't seriously advocate for them without fulling understanding what they are actually going mean in terms of knock-on effects.
To put it crudely, I'm a rapist. I know that if I'm caught and prosecuted I'm going to go to jail and never be released. Ok, in that case I'm just going to rape and kill my victim, since if she isn't alive chances of my crime being discovered and a successful prosecution diminish.
Personally I don't want any part of a country that does 'lock them up and throw away the key' justice. It's completely counterproductive, is driven by nothing other than spite and vindictiveness, and completely undermines the State's moral authority in a similar way to Capital punishment. Leave that nonsense for the real tinpot places. I don't want the UK to be on a par with Iran, China, Saudi and the like when it comes to judicial matters. They are barbarians, we are not.