Owen Paterson, the former Northern Ireland Secretary, has been appointed as a consultant of a company he dealt with while he was pushing for the devolution of corporation tax, it has emerged.
He is one of a number of coalition ministers to have secured jobs with organisations with which they had official dealings in government.
Mr Paterson is taking up a part-time role working as a consultant for Randox Laboratories, which carries out diagnostic work for hospitals, as well as food testing and forensic toxicology.
An investigation by The Telegraph newspaper found more than half a dozen Conservatives and Liberal Democrats had accepted roles with companies and charities they met in their ministerial roles.
The revelations have sparked calls for tighter controls on the "revolving door" between Whitehall and business to prevent ministers cashing in on contacts they acquire while in office.
The rules governing appointments for former ministers are administered by Whitehall's Advisory Committee on Business Appointments.
They prohibit ministers from taking up any jobs that may create "cause for any suspicion of impropriety".
In each case the committee has to consider whether the ex-minister has "been in a position which could lay him or her open to the suggestion that the appointment was in some way a reward for past favours". However, there is no explicit rule banning ministers from taking up jobs with organisations with which they have had direct official dealings during their time in office.
The MP for North Shropshire's contact with Randox began when he was Shadow Northern Ireland Secretary before the 2010 election and continued during his time as Northern Ireland Secretary between 2010 and 2012 as he met firms to discuss the devolution of responsibility for corporation tax to the Northern Ireland Assembly.
Another former minister to have taken up a job at organisations with which they had dealings during their time in government is Steve Webb, the Lib Dem former pensions minister, who is taking up a role at a pensions firm.