The horse sedative Ketamine has been linked to long-term bladder damage.

Stronger laws may be needed to stop one of Britain's fastest growing drugs causing permanent damage to its users, MPs have been warned.

Ketamine, a horse anaesthetic increasingly used as a recreational drug, may need to be reclassified from its current Class C status amid fears it is causing irreversible bladder damage, Professor David Nutt, a key Government adviser, said.

He also told the Home Affairs Committee there was a potential case for a "mature debate" about the potential legalisation of some drugs.

The committee, which is investigating the state of cocaine usage in society, was told many young people were turning to ketamine as a recreational drug because the street strengths of ecstasy and cocaine had declined.

But Prof Nutt warned: "We are seeing a consistent increase in use and we are seeing a very worrying effect in terms of bladder spasms and bladder pain. There is concern that it is causing permanent bladder damage."

Calling for a possible review of laws surrounding the drug, he added: "Class C may be the wrong class."

The panel, sitting at the Houses of Parliament, also heard from Paul Hayes, chief executive of the National Treatment Agency for Substance Misuse, and Dr Neil Brener, from the Priory Clinic.

Mr Hayes, who said £800,000,000 a year was spent on tackling drugs misuse, said the development of a pill to combat cocaine addiction would not provide a "magic" solution.

Last week the committee heard from singer Amy Winehouse's father, who warned that alcohol is leading people on to heroin and cocaine.

Mitch Winehouse, who said his daughter had been sober for a year, also said he supported calls for addicts to be given free heroin on the NHS.