Former ministers and civil servants who enter the private sector should be banned from lobbying for up to five years, the UK’s anti-corruption watchdog has recommended.

The ban should be made legally enforceable and if that should prove impossible or impractical then the government should explore how those who breach the rules could be fined under a new statutory scheme, Lord Jonathan Evans, chair of the Committee on Standards in Public Life, said on Monday.

The recommendations by Evans, which would also apply to special advisers, come in the wake of the Greensill affair, the biggest UK lobbying scandal in a generation.

Evans, a former head of the UK’s domestic security service MI5, said the Advisory Committee on Business Appointments (Acoba), which monitors jobs taken by former government figures, should be allowed to ban ex-ministers from lobbying for up to five years.

“If an applicant had a particularly senior role, or where contacts made or privileged information received will remain relevant after two years, a longer ban may be necessary to ensure former officials lobbying government are not directly benefiting from their time in office when they do so,” Evans said in his report.

He also proposed a two-year ban on any business appointments where the applicant has responsibility for policy, regulation or awarding of contracts relevant to the hiring company.

Earlier this year, the Financial Times revealed that David Cameron, the former prime minister, messaged various senior figures in the Treasury and Downing Street on behalf of Greensill Capital, a finance company which employed him as an adviser.

The government subsequently revealed that there were 56 such approaches by Cameron, who — as prime minister a decade ago — once warned that lobbying was “the next big scandal waiting to happen”.

Greensill went bust in March this year and its relationship with GFG Group, a metals company, is now being examined by the Serious Fraud Office.

There are now nine separate inquiries or investigations taking place into various elements of the Greensill scandal.

The report was part of a general review of “the effectiveness of standards regulation” that began last autumn but the standards committee said it had published its interim findings early because the system was “currently under sustained scrutiny”.

It rebuked the government for failing to provide sufficient information about the lobbying of senior figures. “It is too difficult to find out who is lobbying government, information is often released too late, descriptions of the content of government meetings are ambiguous and lack necessary detail and information in the public interest is often excluded from data releases,” it said.

The report specifically mentioned the Cameron case, pointing out that none of the former prime minister’s “extensive lobbying” on behalf of Greensill was included in any departmental disclosures.

The committee has demanded that ministries release details of lobbying every month rather than every quarter.

It welcomed proposals from the Commissioner for Public Appointments, Peter Riddell, to strengthen his role as an independent arbiter of appointments to government boards.

The committee found the integrity of the appointments system had been undermined by persistent leaking of preferred candidates to the media, which “may discourage suitable candidates from applying for posts”.

It also expressed concerns about the increasing trend of ministers appointing “supporters or political allies” as non-executive directors within departments and called for their appointment processes to be regulated.

The committee was formed in 1994 after the “cash for questions” scandal. Previous governments have adopted many of its recommendations including the creation of the Electoral Commission and the appointment of an independent ethics adviser to the prime minister.