The government is under pressure to stop aid for anti-narcotics programmes in countries where drug traffickers are executed.

The UK leads the way in opposing the use of the death penalty around the world and the government stopped funding Iran's anti-narcotics programme amid concerns that the money was helping to capture drugs mules who were then executed.

Human rights group Reprieve wrote to the deputy prime minister, Nick Clegg, requesting guidance on where the UK's foreign aid was going. The charity's research suggests that Britain is funding and training Pakistan's Anti Narcotics Force.

"As a result of this aid, the ANF and the wider justice system in Pakistan, known to have problems with widespread torture and corruption, is better able to send people to the hangman's noose on drug offences," Reprieve's director, Clive Stafford-Smith, told Clegg. "The ANF itself boasts that 106 prisoners have been sentenced to death on drugs offences in Pakistan alone."

Khadija Shah, a British woman from Birmingham, is potentially facing the death penalty in Pakistan on drugs charges. Her baby, Malaika, who will be one this weekend, has been in prison all her life. Pakistan's new government has promised to end a moratorium on executions.

In his reply, Clegg explained that under guidance issued in 2011 "we can seek assurances that UK co-operation will not lead to torture or prosecutions that result in the death penalty, and have a clear exit strategy if the assurances are not met".

However, Reprieve said it was disappointed that the government had refused to withdraw anti-narcotics funding from countries that practised the death penalty. Such aid was "facilitating the arrest and possible torture and execution of scores of people", said Maya Foa, deputy director of Reprieve's death penalty team.

"It is scandalous that Britain is using taxpayers' money to help other countries send people to the hangman's noose. The 'war on drugs' has failed – instead of stopping the flow of narcotics across international borders, the vast sums of money are facilitating the arrest and possible torture and execution of scores of people. Britain's policy of 'aid for executions' not only undermines the government's stance against the death penalty, but also its obligations to protect its own citizens. It must stop."