With serious assaults at a record high, File on 4 investigates the growing tension within Britain's prisons.

In the first of a new series, BBC Home Affairs correspondent Danny Shaw meets recently released prisoners and families of those inside to hear about their safety fears.

And he talks to the Prison Officers Association about their concerns for the frontline members who they say are facing unprecedented levels of pressure and danger in a "chaotic" system.

The Howard League for Penal Reform has used Ministry of Justice figures to calculate that around 40% of prison officer jobs have been cut - leaving inmates spending longer locked in their cells and less time preparing for their release.

Lawyers and campaigners tell File on 4 that overcrowding and gang activity are adding to a "toxic mix" of problems leading to instability and tension.

Twenty five years after the prison system was shaken by a series of riots centring on Strangeways in Manchester, is a new crisis starting to unfold?

Reporter: Danny Shaw Producer: Sally Chesworth.