"Uniquely in the United Kingdom, methadone ampoules can also be prescribed. Historically, they have at times been a substantial part of opiate substitution treatment in the United Kingdom (e.g. around 30% in the 1970s and approximately 10% in the early 1990s), but they now account for approximately 2% of all methadone prescriptions in England and Wales (Strang et al., 2007). Injectable heroin can also be prescribed in the United Kingdom to heroin addicts as an opiate treatment and has been a treatment option for over 80 years, and this has historically been important. However, over the last 30 years, this practice has become progressively rarer and now comprises less than 1% of all opiate substitution treatment in the United Kingdom. The established method of heroin prescription in the United Kingdom has been as a ‘take-away’ supply, which is then injected in an unsupervised context. In practice, few doctors have prescribed it and few patients have received it (Metrebian et al., 2002)."
European Monitoring Centre for Drugs and Drug Addiction, "EMCDDA INSIGHTS No. 11: New heroin-assisted treatment: Recent evidence and current practices of supervised injectable heroin treatment in Europe and beyond" (Luxembourg: Publications Office of the European Union, April 2012), doi: 10.2810/50141, pp. 134-135.