The prime minister should no longer be the only person who can give permission for ethics investigations into his own conduct and that of ministers, according to a wide-ranging review by the independent committee on standards in public life.

The committee, chaired by former spy chief Jonathan Evans, found that the rules around the conduct of ministers need strengthening, arguing they currently fall “below the bar” for effective standards regulation.

In its “landscape review” of standards in public life, it made nine recommendations, including major changes to the ministerial code of conduct, which is overseen by the prime minister.

It follows widespread calls for reform of the system after Boris Johnson’s previous adviser on ministers’ interests, Sir Alex Allan, resigned after a report into the conduct of Priti Patel, the home secretary, was ignored.

Following an investigation into allegations that Patel engaged in bullying behaviour, Allan found she had “not consistently met the high standards expected of her”, but a government statement said the PM had full confidence in her and considered the matter “closed”.

Since then, Johnson has appointed a new adviser, Christopher Geidt, a former senior aide to the Queen, whose first task was investigating the controversial Downing Street refurbishment that involved Johnson borrowing money from a Tory donor via the Conservative party.

Lord Geidt concluded that Johnson had acted in an “unwise” manner without having breached the rules.

At the moment, the PM is the only person with the power to order investigations into the conduct of ministers, including himself, and is the one to appoint the independent adviser who carries out investigations.

However, the committee on standards in public life said the independent adviser on ministerial interests should instead be appointed by a panel made up predominantly of independent members.

It also recommended that the adviser should be able to initiate their own investigations, have the authority to determine breaches of the code and see their report published within eight weeks of submission to the PM.

On the ministerial code itself, the report said it needed to have a constitutional footing laid down in law, with any revisions subject to advice from the independent adviser, and possible sanctions for breaches should be set out including apologies, fines and asking for a minister’s resignation.

The committee also recommended a strengthening of the advisory committee on business appointments (Acoba), which governs the revolving door between government and the private sector by advising on lobbying and jobs taken on by former ministers and officials.

It said the current ban on officials and ministers lobbying for two years after leaving their post should be able to be extended to up to five years, and any work for a lobbying firm should be included in the ban, rather than just a prohibition on direct lobbying.

“The lack of any meaningful sanctions for a breach of the rules is no longer sustainable,” the report said, suggesting injunctions against lobbying work could be sought or means of recouping severance or pension payments.

Thirdly, it said there needed to be further reforms to the powers of the commissioner for public appointments, which oversees jobs for top civil servants and at public bodies, to make sure appointment panels are independent.

Evans, a former director general of MI5, said the committee had concluded that the “current system of standards regulation is overly dependent on convention”. The recommendations were necessary to “restore public confidence in the regulation of ethical standards in government”, he added.

In response, Dave Penman, the general secretary of the FDA union for senior civil servants, said the recommendation that the independent adviser should be able to initiate investigations was “essential if the code is to have a meaningful independent function”.

“There can be no hiding from the fact that the current prime minister has undermined confidence in the ministerial code as a meaningful regulator of ministerial conduct,” Penman said.

The recommendations were endorsed by Sir John Major, the former Tory prime minister who first set up the committee.

In a foreword, Major said the committee “makes many important recommendations that I hope will be approved by the government – and, where necessary, parliament – and then implemented”.

Angela Rayner, the deputy Labour leader, said her party welcomed the report, and many of its recommendations had previously been called for by Labour.

“Boris Johnson and his Conservative colleagues’ actions have repeatedly undermined standards in our public life,” she said.

“The system that is supposed to uphold the ministerial code, lobbying rules, business appointments, public appointments and transparency is clearly unfit for purpose.

“Ministers have disregarded the rules and it is about time for a radical overhaul of the system.”