Ministers could be banned from lobbying for up to five years after leaving office and also face possible penalties if they break the rules, the anti-corruption watchdog has said.

Jonathan Evans, the chair of the committee on standards in public life, made the proposal in an emergency review published on Monday in the wake of the Greensill scandal.

The intervention by Lord Evans, a former head of MI5, is a response to claims that the rules continue to be flouted by former ministers, special advisers and senior civil servants once they leave office. His report demands an overhaul of the rules in an attempt to stop the revolving door in Whitehall that allows them to use their contacts and expertise for private gain.

Under current rules, ministers and senior civil servants are in effect banned from lobbying their former colleagues for two years after leaving their post.

The committee has also raised concerns that the system of appointing to public bodies may be leaning towards ministerial patronage and away from “merit”, following rows over Boris Johnson’s attempts to impose the former Daily Mail editor Paul Dacre as the head of Ofcom.

No 10 is expected to wait until the final report from the committee later this year before saying which recommendations it might accept.

The report names David Cameron, the former prime minister under whom Evans served for three years as head of MI5, in concluding that the current rules are inadequate, and says ministers should disclose informal lobbying over WhatsApp and text messages in future.

Cameron texted Rishi Sunak, the chancellor, on behalf of Greensill Capital, a finance firm that employed him as a lobbyist and the collapse of which has put thousands of jobs at risk. He asked the government to change the rules to allow it to receive Covid corporate financing facility loans.

It has since emerged that he subjected Matt Hancock, the health secretary, and other ministers to a deluge of WhatsApp messages and texts, including 56 messages over a single Covid loan scheme.

As there were more than two years between his resignation as prime minister and taking up his role at the failed financial firm, Cameron’s actions were permissible under current rules.

Lex Greensill, an Australian financier, was given access to 11 Whitehall departments, having previously been appointed as an official government adviser without any transparency.

Cameron told MPs last month there was “absolutely no wrongdoing” in his lobbying attempts, but accepted that former prime ministers must “act differently”.

The report forms part of the committee’s “landscape review of standards”.

The committee also proposes: introducing anti-lobbying clauses into the employment contracts of ministers, special advisers and civil servants; designing a system of possible civil penalties for rule-breakers; banning ministers from taking jobs for two years in sectors over which they had direct responsibility in office; and giving the appointments watchdog the power to apply tailored restrictions, including banning ex-ministers from taking certain jobs for up to five years “where appropriate”.

It also calls for new rules so that the government releases details of lobbying every four weeks, rather than quarterly; and regulating the appointment of non-executive directors to Whitehall departments amid fears politicians are appointing “cronies”.

In a foreword to the report, Evans says: “We have found that four areas of standards regulation require significant reform: the ministerial code and the independent adviser on ministers’ interests, the business appointment rules and the advisory committee on business appointments (Acoba), transparency around lobbying, and the regulation of public appointments.”

The report says the powers of the commissioner for public appointments, a position occupied by Peter Riddell, need to be strengthened if the integrity of the process is to be upheld.

“Reforms are necessary to ensure the commissioner has sufficient powers to uphold the integrity of the process by which a list of appointable candidates is produced, from which ministers can make their choice,” it says.

It also criticises the unregulated appointments of non-executive directors (NEDs). Michael Gove was criticised last year after appointing three close Vote Leave allies, Baroness Finn, Henry de Zoete and Gisela Stuart, to roles in the Cabinet Office.

“There is an increasing trend amongst ministers to appoint supporters or political allies as NEDs. This both undermines the ability of NEDs to scrutinise the work of their departments, and has a knock-on effect on the appointments process elsewhere, as NEDs are often used on the assessment panels for other public and senior civil service appointments. The appointment process for NEDs should be regulated,” the report says.