"It is highly alarming that the police and prison service have in effect ceded the airspace above two high-security prisons to organised crime gangs," chief inspector of prisons Charlie Taylor said in reports published Tuesday after inspections of Manchester prison in northwest England and Long Lartin prison in western England.

The gangs "are able to deliver contraband to jails holding extremely dangerous prisoners," with "catastrophic levels" of drugs present at the prison in Manchester, he warned.

"The safety of staff, prisoners and ultimately that of the public is seriously compromised by the failure to tackle what has become a threat to national security," added Taylor.

"The prison had a serious problem with drugs, weapons, mobile telephones, and even takeaway meals being delivered by drones to cell windows," the report on Manchester prison said.

It added some 220 drone sightings had been seen at the jail in the past year "by far the highest across all prisons in England and Wales".

Taylor told the BBC that "knives indeed are getting in" stashed on drones that have a payload of up to three pounds (1.3 kilos), with some inmates having organised deliveries of fearsome "zombie" knives, known for long blades with serrated edges.

"It's entirely possible that if somebody was determined enough they could get a gun in," he added.

The inspections uncovered "thriving" drug economies in both prisons, with nets and security cameras allowed to fall into "disrepair", the HM Inspectorate of Prisons said in a statement.

In Manchester, inmates had burned holes in windows to receive drone deliveries, while drones carrying "large payloads of illicit items" were allowed to enter Long Lartin prison.

More than half of prisoners told inspectors it was "easy" to get drugs and alcohol.

A Ministry of Justice spokeswoman said the Labour government, which came to power in July, had "inherited prisons in crisis -- overcrowded, with drugs and violence rife.

"We are gripping the situation by investing in prison maintenance and security, working with the police and others to tackle serious organised crime, and building more prison places to lock up dangerous criminals," she added.