Pressed on how many foreign prisoners could be returned, Burnham said it was “hundreds”. Government figures show there were 10,134 foreign nationals in custody as of late June, representing 12% of the prison population.
The government has said powers will be implemented early next year to deport some foreign criminals immediately after sentencing.
Those powers would block foreign prisoners from ever returning to the country while “keeping those in prison for the most serious crimes locked up for a substantial period before they are removed”.
The government is not thought to have signed any additional prisoner returns agreements with other countries.
It is understood that work has also begun to create more cells in existing prisons by adapting space used for other purposes, but that is also expected to take months.
None of the measures announced by Burnham are likely to create much additional prison capacity by the time the first batch of prisoners are released early in October.
The prime minister is said to have taken a “political decision” to use some of the remaining capacity in the prison system to ensure the changes announced today could be implemented immediately.
In addition to those in jail for manslaughter, the prime minister said prisoners convicted of indecent assault offences and death by dangerous driving will also remain in prison.
Historic child sex offences and causing or allowing the death of a child will also be exempted from the early release scheme, while new “restriction zones” to better protect domestic violence survivors from perpetrators released early will be introduced.
The justice secretary is expected to give a more precise figure for how many people will be affected when he gives a statement in Parliament on Tuesday.
In response to Sunday’s announcement, Conservative shadow justice secretary Nick Timothy accused Labour of avoiding parliamentary scrutiny of the changes.
“The government must delay the scheme, bring forward emergency primary legislation and exclude the worst offenders properly,” he said.
Liberal Democrat justice spokesperson Jess Brown-Fuller MP said the uncertainty over the early release scheme had been “unforgivable”.
“PC Andrew Harper’s killers will now remain in prison, but this should never have been in question,” she said.
Dame Nicole Jacobs, Domestic Abuse Commissioner for England and Wales said she remains “deeply concerned about the number of abusers who will still be eligible for early release”.
“Victims and survivors will still be forced to take measures to protect themselves from dangerous abusers because the government and our criminal justice system cannot”, she added.
