Prison staff have been unable to work after being overcome with fumes from a dangerous drug being used by inmates.

Up to four officers at HMP Rochester were sent home after falling ill, and it is thought at least one had to receive hospital treatment after being affected by smoke from a legal high called Spice.

The substance, which has been linked to 19 deaths behind bars, is similar to cannabis but believed to be about 100 times more powerful. It can cause vomiting, seizures and psychosis.

The use of the drug at Rochester is said to be rife, with packages being thrown over the prison wall at pre-arranged times.

A source close to the jail said: “The staff are having one hell of a problem with this particular legal high.

"There was an incident where the fumes were so great they affected staff, including one who had a heart condition.”

Spice can be smoked or consumed in liquid form in vapour cigarettes.

It is often called “fake weed” because some of the chemicals in it are similar to marijuana but its effects are unpredictable.

The drug can raise blood pressure and restrict blood flow to the heart, leading to a heart attack.

A report by the Prisons and Probation Ombudsman, published last year, found Spice and a similar drug called Black Mamba were factors in at least 19 prisoner deaths across the country between 2012 and 2014.

It is popular behind bars because it is cheap, highly potent and often does not show up in urine tests.

During the most recent inspection of HMP Rochester, inmates were seen clearly under the influence of drugs but going unchallenged by staff.

The chief inspector said there was evidence of “considerable amounts” of legal highs in the prison with large packages being thrown over the wall, and inmates reported it was easy to get hold of drugs.

A Prison Service spokesman said: “Governors use sniffer dogs, cell searches and drugs tests to find drugs in prison and punish those responsible.

“HMP Rochester staff are also working with police to restrict the supply of drugs.”

He added:“We have passed laws so that those smuggling packages over prison walls, including drugs, face up to two years in prison.

“However, it is clear 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.”