An audacious breakout attempt at a Midland jail saw bolt cutters being flown to prisoners using a drone.
The escape attempt at HMP Featherstone, in Staffordshire, saw the aircraft's remote operator unload the tools near the prison's perimeter fence.
But the bizarre escape plot failed when guards alerted police – who seized the kit before it could be hauled in by lags.
The drone also contained banned mobile phones and a consignment of drugs, said to include the deadly super-strength "legal high" Spice.
A police probe into the smuggling bid was under way this week.
A source said: "It was only by luck that a staff member saw the drone and witnessed it dump its load outside the fence.
"The theory is the operator made a mistake and the parcel should have been unloaded inside the jail."
The drone was found on Sunday, March 6, at the category C secure jail, which was the scene of a rare escape over the wire in April 2015.
Burglar Joseph Moss, 22, from Birmingham, was on the run for a week before being recaptured.
Prison bosses fear the bolt cutters were part of a plan for a mass escape.
The latest incident follows a surge in the use of aerial drones to smuggle contraband into prisons.
Figures for 2015 show 33 of the unmanned crafts were discovered in or around jails in England and Wales – up from just two the previous year.
Glyn Travis, assistant secretary of the Prison Officers Association, said: "The threat from drones is escalating.
"In this case, the discovery of bolt cutters suggests a plan to cut through the perimeter fence. There can be no doubt that an inmate inside had ordered the equipment for a possible escape bid."
Mr Travis said the use of drones to smuggle drugs and mobiles undermined jail security.
He added: "The POA is calling for increased staffing levels to tackle the threat of drones."
A Prison Service spokesman said: "Vigilant staff at HMP Featherstone successfully stopped illicit items getting into the hands of prisoners. The incident is being investigated by the police.
"The Government has introduced new legislation meaning anyone found using drones to smuggle contraband can receive a two-year sentence.
"However, more must be done, which is why the justice secretary has asked the Ministry of Justice to look at how we can ensure prisons have the right tools in place to tackle this kind of problem."
