Cash-strapped jails are facing a new crisis – people breaking in.
In one case, a 13-year-old boy strolled into an open prison to deliver drugs.
Unions say security is so lax at other low-category sites that criminals drop off takeaway food to pals still inside.
The Prison Officers Association said Tory cuts had left some Category D jails with just three guards over night.
The incidents came to light after one prisoner was battered by intruders at HMP Spring Hill, in Aylesbury, Bucks.
Thugs burst in and launched a brutal 10-minute attack before fleeing – with the lag who had ordered the assault.
The prisoner returned voluntarily 48 hours later. Police are probing the incident, earlier this month.
Mick Pimblett, POA assistant general secretary, said: “People have gone into open prison to deliver drugs and even takeaways.
“This demonstrates the difficulties prison officers face in securing open jails, particularly at night-time. We are under-resourced and under-staffed. Cuts to budgets and staff put the prison community and public at risk.”
Mr Pimblett said the 13-year-old was held at Category D Thorne Cross prison, in Warrington, Cheshire, this year.
MP Daisy Cooper, Lib Dem justice spokeswoman, said: “Conservative cuts have caused havoc. Because of overcrowding and under-staffing, the prison system is unable to cope. We need an urgent intervention to end this shambles.”
She called for community-based sentences “that actually work”.
Figures show two inmates fled open jails every week over the past five years, including 22 murderers and 18 rapists.
HMP Sudbury, Derbys, had the most runaways – with 108.
Of Spring Hill, a Prison Service spokesman said: “A prisoner was treated in hospital after an incident involving intruders. Police are investigating.”