Labour has urged ministers to respond to claims of stifling war crimes investigations after it emerged that no prosecutions have been launched relating to allegations of abuse at a British army base in Iraq in 2003.

The shadow attorney general, Shami Chakrabarti, said the allegations of murder, torture and sexual abuse deserved “anxious scrutiny” by the international criminal court (ICC). Downing Street denies any cover-up has taken place.

Chakrabarti said: “To cover up abuse only undermines Britain’s reputation, military morale, and leaves our own people more vulnerable to abuse by enemy hands in the future. Now ministers must answer these serious charges that they misled the public and stifled war crimes investigations by the Royal Military Police.”

The Conservatives want to introduce a presumption against war crimes prosecution for veterans of Iraq and Afghanistan, and Boris Johnson promised during his Tory leadership campaign that he would legislate to end “unfair trials”.

The allegations, which surfaced after an investigation by BBC Panorama and the Sunday Times, suggest there remain serious unresolved issues relating to the conduct of the military dating back nearly 20 years.

The investigation drew on cases examined by the Iraq historic allegations tribunal (Ihat), which was shut down by ministers in 2017. Detectives who worked at Ihat said they found evidence of abuse at Camp Stephen, run by the Black Watch, 3rd Battalion, Royal Regiment of Scotland, in Basra, in southern Iraq.

The investigators found evidence that two Iraqi men were tortured at the camp and died with bags tied over their heads. This summer, special British military prosecutors decided no one would be prosecuted.

Downing Street said claims that the government covered up allegations of unlawful killings and abuse by British soldiers in Afghanistan and Iraq were untrue and it defended the military.

The prime minister’s spokesperson said: “Our military served with great courage and professionalism in Iraq and Afghanistan and allegations that the MoD [Ministry of Defence] interfered with investigations or prosecution decisions into the conduct of UK forces are untrue.”

Ihat was shut down in 2017 after Phil Shiner, a solicitor who had taken more than 1,000 cases to the tribunal, was struck off from practising law amid allegations that he had paid people in Iraq to find clients for the UK courts.

The ICC has said it may investigate the British military. It said it took the claims made in the Panorama/Sunday Times investigation “very seriously”, according to the BBC.

“The ICC said it would independently assess the BBC’s findings and begin a landmark case if it believed the government was shielding soldiers from prosecution,” the corporation said.

The court, which has an open inquiry into the conduct of British troops, has previously concluded it was credible that British troops committed war crimes in Iraq related to the mistreatment of detainees.