Former ministers can exploit loose and ambiguous guidelines on lobbying to cash in "with impunity" on their inside knowledge of Westminster, a Commons committee warns.

Demanding tough new rules and a statutory register of lobbyists, the MPs registered alarm that the "revolving door" between government and business was harming public trust in politics.

Tony Blair – now a consultant for JP Morgan Chase and Zurich Financial Services – is among several senior politicians who have taken private sector jobs. Others include the former cabinet ministers Patricia Hewitt, Hilary Armstrong and Ian McCartney.

The Public Administration Select Committee said it was worried about former government ministers being headhunted to lobbying jobs soon after they left office – particularly when they were still MPs.

It said: "Former ministers can, within all existing rules, use their former ministerial position to help them to gain access for private interests." It cited the example of Stephen Ladyman, a former Transport minister who is now paid up to £15,000 a year to advise Itis Holdings, a company that sells traffic information. It said he had used his former government post "as a way of introducing himself when lobbying on behalf of Itis".

Former ministers are required to abide by advice from a Whitehall committee before taking up private sector jobs linked to their government posts. But the public administration committee concluded that the guidance was inconsistent and vague and demanded that all lobbying activity be monitored by a watchdog.

It said: "Former ministers in particular appear to be able to use with impunity the contacts they built up as public servants to further a private interest. We think this is unacceptable, particularly where they continue to be paid from the public purse as sitting members of Parliament."

The committee ruled out a lifetime ban on such appointments but recommended an extended period of several years before former ministers and public servants could use their contacts and sensitive information to further their own and others' interests.