Guiding illicit drug legislation in the United Kingdom is the Misuse of Drugs Act 1971 (MDA).  This legislation and associated regulations control the use of both legal prescription drugs and illegal drugs.  Drugs are classified as either A, B or C to reflect the degree of harm they are considered to cause to the individual or society when abused.  Each class has different maximum penalties that apply to prohibited activities. 

• Class A is reserved for the more harmful drugs; severe penalties may apply.  This class includes (among others) heroin, morphine, methadone, cocaine, opium, Ecstasy and LSD.
• Class B includes less potent opioids like codeine, amphetamines and barbiturates.
• Class C is reserved for drugs that are considered the least harmful such as marijuana, tranquilizers, less potent stimulants and mild analgesics.

The Home Secretary can change the classification of drugs through delegated legislation.  Any such change must be preceded by consultation with the Advisory Council on the Misuse of Drugs.  The Council is a statutory body which reviews drugs which have the potential to be abused advises government on measures necessary for the prevention of drug misuse.
 
The Drug Trafficking Act 1994 was adopted to enable the UK to meet its obligations under the United Nations Convention against Illicit Traffic in Narcotic Drugs and Psychotropic Substances 1998 (The Vienna Convention).  It creates offences in connection with laundering and handling of the proceeds of drug trafficking, and introduces confiscation measures.  Modeled after U.S. civil asset forfeiture laws, the burden of proof is placed on the defendant to prove that the assets were lawfully acquired and applies the civil standard of proof on the balance of probabilities.

Reform Debate in the UK 
 
The use of marijuana for medicinal purposes has a long history in the UK.  It was prescribed as a medicine in the UK until 1973.  At that time, it became a drug that could not be legally used as a medicine and today its medicinal use remains prohibited.  The Science and Technology Committee of the House of Lords recommended that marijuana be made available for medicinal purposes in a 1998 report.  This recommendation was rejected by the government which indicated that before such a change could be considered, the safety and efficacy of marijuana would have to be demonstrated.  G.W. Pharmaceuticals has been given permission to grow marijuana with the aim of developing a marijuana-based medicine; clinical trials have commenced in the UK.

In March 2002 a report from the Advisory Council on the Misuse of Illicit Drugs gave British Home Secretary David Blunkett's proposal to downgrade marijuana to "low-risk" Class C status the go ahead. While acknowledging that marijuana can be harmful, the report noted that marijuana poses fewer risks than alcohol or tobacco.  Alcohol was singled out as posing far greater societal risks because it encourages risk-taking and leads to aggressive and violent behavior.  According to the report marijuana "is not associated with major health problems for the individual or society."  The Advisory Council's acknowledgement that marijuana should be reclassified came shortly after the release of a study by the South Bank University's Criminal Policy Research Unit that found that decriminalizing marijuana would save roughly $71 million a year and free up the equivalent of 500 police officers who could instead concentrate on violent crime.

Prescription heroin maintenance is another hot topic in the United Kingdom. The practice of prescribing heroin to addicts was standard in England from the 1920s to the 1960s. In response to political pressure from the United States, heroin maintenance was severely curtailed in 1971 when passage of the Misuse of Drugs Act added burdensome regulations. Government disapproval led to a sharp decline in the practice among private physicians. The loss of a controlled distribution system and subsequent creation of an unregulated illicit market allowed the number of heroin users to skyrocket from fewer than 2,000 in 1970 to upwards of 300,000 today. What was once discouraged is now being actively promoted, in large part due to a perceived increase in heroin-related crime. The Association of Chief Police Officers and British Home Secretary David Blunkett have both voiced support for heroin maintenance as a means of breaking the link between heroin and crime. In 2002, the Home Office recommended that heroin users be able to receive pharmaceutical grade heroin from general practitioners as part of a major government initiative to tackle the problem of illegal drugs use in the United Kingdom.