The number of prisoners in England and Wales should be cut by almost a half, two former home secretaries and a former deputy prime minister have urged.
Former Tory home secretary Kenneth Clarke, Liberal Democrat MP Nick Clegg, deputy prime minister in the coalition government and Jacqui Smith, who served as Labour's home secretary between 2007 and 2009, called on the Government to act to curb the "escalating prison population", in a letter published in The Times.
The cross-party trio said the population of prisons in England and Wales had "gone well beyond what is safe or sustainable" and that numbers should be reduced from around 85,000 to 45,000.
The call for action follows last week's riot at HMP Birmingham, which saw hundreds of inmates wreak havoc in the jail over more than 12 hours of chaos.
The politicians said the violence was "a wake-up call for this country".
"To restore order, security, and purpose to our jails, Ministers should now make it their policy to reduce prison numbers," the letter said.
"We want to see the prison population returned to the levels it was under Margaret Thatcher, herself no 'soft touch'.
"That would mean eventually - not overnight, but safely over the course of several years - reducing prison numbers to around 45,000.
"If the tide is not turned soon, the prisons crisis will do untold damage to wider society."