Changes to the ministerial code go beyond "mere tidying up" and instead show a "contempt for the rule of international law", the former head of the Government Legal Service has said.
The latest edition of the code – which outlines the conduct expected of ministers – was published earlier this month, and omits a reference to ministers being bound by international law.
The 2010 version of the code said ministers had a duty to abide by the law, "including international law and treaty obligations". But the updated guidance refers only to "the law". The Cabinet Office has said the code continues to account for ministers' international obligations.
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But Sir Paul Jenkins, who served as Treasury solicitor and head of the Government Legal Service until March last year, questioned the rationale for the changes in a letter to the Guardian.
"It is disingenuous of the Cabinet Office to dismiss the changes to the ministerial code as mere tidying up," he wrote.
"As the government’s most senior legal official I saw at close hand from 2010 onwards the intense irritation these words caused the PM as he sought to avoid complying with our international legal obligations, for example in relation to prisoner voting.
"Whether the new wording alters the legal obligations of ministers or not, there can be no doubt that they will regard the change as bolstering, in a most satisfying way, their contempt for the rule of international law."
Meanwhile, campaign group Rights Watch has written to the prime minister outlining its objections to the amendments.
"For the government to erase from the ministerial code the starting presumption that its ministers will comply with international law is seriously concerning,” the group's director Yasmine Ahmed said.
"It evidences a marked shift in the attitude and commitment of the UK government towards its international legal obligations."
A spokesperson for the Cabinet Office, however, said the changes were made to "bring the code more in line with the civil service code", and said the reference to legal compliance "includes international law".
"The obligations remain unchanged by the simplified wording," the spokesperson added. "The ministerial code is the prime minister’s guidance to his ministers on how they should conduct themselves in public office.”