Britain’s spies stand accused of continuing to share intelligence obtained under torture, in breach of official guidance. The damning claim, outlined in a letter to the foreign secretary, Boris Johnson, is made by his Labour shadow, Emily Thornberry, and the shadow attorney-general, Shami Chakrabarti.

They point to hitherto unpublicised figures buried in the latest annual report from the Intelligence Services Commissioner (ISC), who has a statutory duty to review the way MI5, MI6 and GCHQ share intelligence.

The use of intelligence obtained abroad is governed by an official document, the Consolidated Guidance on the Detention and Interviewing of Detainees Overseas.

According to the latest ISC report, released in the run-up to last Christmas, in 2016 the three agencies and the Ministry of Defence felt a need to consider the guidance in 921 cases – more than double the number the previous year.

Thornberry and Chakrabarti write: “The commissioner’s most recent report reveals a doubling of cases considered under the Consolidated Guidance, compared with the last three years, and an unprecedented number of acknowledged failures to apply the Guidance.”

Sir Mark Waller, the then commissioner, who stood down last year, found that GCHQ had failed to follow the guidance in 35 cases.

The letter states: “Even worse, in eight of those cases, it was found that the intelligence was shared despite the fact that the Guidance should have prohibited further action – presumably as a result of what were serious risks of torture or other ill-treatment.”

The revelation that British spies are sharing intelligence that may have been obtained under torture with other parties is embarrassing to the government. Last month it gave an unreserved apology to Abdel Hakim Belhaj and Fatima Boudchar, who were abducted by the CIA with British help and rendered to Libya.

At the time, the attorney-general Jeremy Wright said the government had “enacted reforms to ensure that the problems of the past will not be repeated.” But Thornberry and Chakrabarti said the ISC report suggested that the Belhaj case was not an isolated one. “The number of cases in which the Guidance was wrongly ignored suggest there remain serious problems in terms of the agencies’ compliance with it,” they write.

The government is currently reviewing the guidance after criticism from Waller and others. But human rights groups and politicians from all parties have concerns about the scope of the review.

“The ISC figures, snuck out just before Christmas, show that the UK’s policy on handling torture-tainted evidence simply isn’t fit for purpose,” said Dan Dolan, head of policy at human rights watchdog Reprieve. “If we’re to prevent UK involvement in torture we need proper reform of this policy, which will not be delivered through a piecemeal internal review steered by officials and intelligence agencies. There must be a full public consultation. The foreign secretary can no longer simply dismiss public concern over torture.”

The Lib Dems, the SNP, the Green MP Caroline Lucas and Ken Clarke, chairman of the all-party parliamentary group on extraordinary rendition, all want the review to be a broad consultation with input from outside experts and organisations. Writing on the Conservative Home website, Clarke said: “The current review of the Guidance is particularly timely. With Donald Trump having pledged to reintroduce waterboarding and ‘a hell of a lot worse’, it is more important than ever that the UK has as robust a policy as possible to prevent future involvement by our intelligence services in such activities.”

Trump’s appointment of Gina Haspel as the new director of the CIA has further fuelled these concerns.

Last week, in what was described as “a significant anti-torture ruling”, the European court of human rights held that Lithuania and Romania violated the rights of Abu Zubaydah and Abd al-Rahim al-Nashiri by allowing them to be detained at CIA “black sites” on European soil. Haspel oversaw the torture of Nashiri at a CIA black site in Thailand in 2002.

Thornberry and Chakrabarti write: “With the recent installation of a new CIA director heavily implicated in the US torture and rendition programme, the UK government must demonstrate that it takes its compliance with the international prohibition on torture seriously. It must set out and publicly consult on its plans to ensure UK intelligence officers are not made complicit in abuses overseas.”

A government spokeswoman said: “The UK stands firmly against the use of torture. We do not participate in, solicit, encourage or condone the use of such techniques for any purpose and we have robust oversight arrangements in place. It is open to the public and civil society to submit their views at any time to the government.”