The rampant use of designer drugs in prisons is placing local ambulance services under strain as paramedics are increasingly called out to tend to criminals who have used the substances, a watchdog has warned.
In one incident involving so-called "legal highs" all of the available crews in a community had to be deployed to a jail at the same time, a report by HM Inspectorate of Prison (HMIP) found.
A large number of adult male facilities have reported incidents when emergency medical assistance had been required for prisoners who had used synthetic cannabis drugs such as "mamba" and "spice".
Incidents are so common that inmates in a number of establishments have adopted the nickname "mambulances".
Paramedics were called to attend to prisoners having fits, blackouts and other adverse symptoms. In some instances multiple ambulances were dispatched when several prisoners needed treatment at the same time.
The HMIP report said: "This not only put individual prisoners at risk, but also placed excessive demand on resources that were required for the local community too.
"Some prisons have required so many ambulance attendances that community resources were depleted."
An episode at HMP Wealstun in Yorkshire was singled out.
Chief Inspector Nick Hardwick said: "They were having so many health emergencies caused by the use of NPSs (new psychoactive substances) that basically all of the available ambulances in the community on one occasion were at the prison dealing with prisoners in health crisis.
"So actually there wasn't the resilience, if there had been something happening in the community they weren't there to deal with that because they were in the prison.
"It is a big issue."
A dramatic flood of NPSs into prisons has been linked to rising levels of violence and 19 deaths behind bars.
The HMIP study, which drew on evidence of 61 inspections and a survey of nearly 11,000 prisoners, concluded that they are now the most serious threat to the safety and security of jails.
:: Offenders on licence are deliberately breaking their terms of release in order to return to prison to smuggle drugs in for thousands of pounds.
:: Substances are sometimes hidden in bodily cavities in order to evade security checks, while drones and catapults are being used to fire packages over prison walls.
:: Smuggling operations are increasingly sophisticated, with one arrangement involving the use of potatoes for tests shots to see where packages would land using the help of a "spotter" inside the prison.
:: Inmates are being used as "spice pigs" to test new batches.
:: Drug debts are sometimes enforced on prisoners' friends or cell mates in prison, or friends and family on the outside.
:: Synthetic cannabis distribution is seen as "low risk" but "high profit" and money from drug supply in prisons may be used to fund organised crime in communities.
Mr Hardwick accused the government of being "too slow" to respond to the "real and current" threat posed by legal highs behind bars.
"We think we need ministers to actually lead a process of keeping patterns of drug use under review and making sure there's an adequate response.
"Otherwise we think there is a danger that complacency will creep into the system."
Testing technology described by ministers as a "game changer" is set to be rolled out, while a new law is being introduced to target smugglers.
Mr Hardwick said that drug issues in prisons change rapidly, warning against the belief that new measures will solve the problem.
"What will happen is the problem will shift to other areas."
A Prison Service spokeswoman said: "We take a zero tolerance approach to drugs in prison and there are already a range of robust measures in place to detect drugs, including the use of sniffer dogs, searches of cells and mandatory drugs tests.
"We recently introduced tough new laws which will see those who smuggle packages over prison walls, including drugs, face up to two years in prison.
"Those who involve themselves in the distribution of drugs in our prisons should know that they will face prosecution and extra time behind bars."