Boris Johnson has been accused of watering down the rules for ministers after it was made clear they will not automatically lose their jobs if they breach the Ministerial Code.

A Government policy statement said it was “disproportionate” to expect ministers to resign or face the sack for “minor” violations of the code’s provisions.

Instead it has been updated, giving the Prime Minister the option of ordering a lesser sanction such as “some form of public apology, remedial action or removal of ministerial salary for a period”.

It had previously expected that ministers should go if they were found to have breached the code.

At the same time Mr Johnson has drawn backing from allowing his independent adviser on the code, Lord Geidt, to mount investigations into possible violations on his own initiative.

Under his revised terms of reference, there will be an “enhanced process” to enable him to initiate inquiries, but he will still require the Prime Minister’s consent before going ahead.

“Reflecting the Prime Minister’s accountability for the conduct of the executive, it is important that a role is retained for the Prime Minister in decisions about investigations,” the statement said.

The changes come just days after the final report by the senior civil servant Sue Gray into lockdown parties in Downing Street led to renewed calls for Mr Johnson to resign.

The Prime Minister is now facing an inquiry by the Commons Privileges Committee into whether he misled Parliament into what happened.

Labour said Mr Johnson had removed all references to “integrity, objectivity, accountability, transparency, honesty and leadership in the public interest” from his own foreword to the code to “save his own skin”.

Deputy leader Angela Rayner said: “This Prime Minister is downgrading and debasing the principles of public life before our very eyes.

“In a week when Boris Johnson’s lies to Parliament about industrial rule-breaking at the heart of Government were finally exposed, he should be tendering his resignation but is instead watering down the rules to save his own skin.

“Once again, Boris Johnson has demonstrated he is not serious about his pledge to address the scandal and sleaze engulfing his Government or the frequent and flagrant breaches of standards and rule-breaking that have taken place on his watch.”

Liberal Democrat chief whip Wendy Chamberlain said: “This is an appalling attempt by Boris Johnson to rig the rules to get himself off the hook.

“The Prime Minister shouldn’t be allowed to decide on his own punishment – with zero accountability.

“This is making him judge and jury in his own case.

“If the Privileges Committee finds Boris Johnson lied to Parliament, surely Conservative MPs will have no choice but to sack him.”