With shortages of the drugs used to carry out lethal injections in the USA now at critical levels, supplies are now being bought in from other countries, including the UK.

The exports are raising ethical concerns, particularly in cases where the exporting country does not legally permit the death penalty.

For example, the BBC reports that a small London-based pharmaceutical distributor supplied sodium thiopental, potassium chloride and pancuronium bromide - all medicines used for lethal injections - to Arizona State Prison in September 2010.

It is thought the drugs may have been used in the execution of convicted murderer Jeffrey Landrigan in October. The charity Reprieve UK has provide documentary evidence that Acton-based Dream Pharma - which operates at the rear of a driving school - supplied around £4,500-worth of the drugs to the prison, enough to execute "at least 10 prisoners." UK suppliers have also exported lethal injection drugs to Arkansas and California, it says.

The UK's Business Innovation and Skills Secretary Vince Cable placed export controls on sodium thiopental in late November, but has yet to take action on the other two drugs, says the charity, which is also calling on drugmakers to "assist in the task of preventing their drugs from being used to kill people."

To date, just one company, Hameln Pharma, has acted to prevent the use of its drugs in this way, according to Reprieve.