BRIAN COWEN is expected to announce a major cabinet shuffle today, after a sixth senior member of his cabinet handed in his resignation this morning.

Following the announcement by Minister for Health, independent minister Mary Harney, that she was stepping down - saying it was inappropriate for her to remain in cabinet if she was not running in the next general election - three other ministers who are also retiring sent in their letters of resignation last night.

Those ministers are Transport minister Noel Dempsey, from Meath West; Justice minister Dermot Ahern, from Louth, and Tony Killeen, the Minister for Defence, from Clare.

And this morning, Enterprise minister Batt O'Keeffe added his name to the departing ranks, with RTÉ News confirming that he, too, was not going to contest the next election - and that he, too, was therefore leaving the cabinet.

Coming just over 36 hours after Foreign Affairs minister Micheál Martin handed in his own resignation, which was accepted by President McAleese yesterday morning, the latest wave of resignations now means that over a third of the seats around the cabinet table now lie vacant - almost certainly prompting Brian Cowen to take immediate action to fill those seats.

The Irish Times reported that in the aftermath of Harney's resignation - confirming that she was not running to retain her seat in Dublin Mid West, a seat she has held since 1981 - Fianna Fáil sources had suggested that other ministers may be set to formally step down, allowing Cowen to continue with a major reshuffle in spite of the Green Party's unease.

Gormley had told RTÉ's Six One news - when there was just one cabinet vacancy - that he expected his party would be consulted before any ministry would be filled, but seemed to favour the straightforward promotion of a junior minister or backbencher, rather than a major reshuffle.

Harney's resignation was confirmed on the later 9pm bulletin - and two hours later, a government spokesman confirmed that the three Fianna Fáil ministers had also tendered their resignations.

In Dermot Ahern's case, it was speculated this morning, that resignation had been offered several months ago as Ahern's arthritis became a greater concern, but Cowen had chosen not to pursue it until now.

Gormley and Cowen spoke this morning to discuss the cabinet positions, RTÉ reported, and Gormley is expected to consult with his Green Party colleagues later today.

Opposition parties have said the spate of resignations should trigger an immediate general election, rather than the appointment of new ministers to fill jobs simply for a number of weeks.

A government statement said the Taoiseach would recommend to President McAleese that she formally accept the resignations of the four ministers - though the government press office is still to confirm O'Keeffe's resignation.

If the positions are not filled today, it is likely that they will remain vacant over the weekend, with a cabinet meeting usually held before ministerial vacancies are filled.

The Green Party's unease at a full cabinet reshuffle - which may promote ministers and TDs who could face electoral difficulties otherwise - was underlined this morning, when Paul Gogarty wrote on his blog that the co-ordinated resignation of the ministers "smacks of an orchestrated plan that has little to do with the country's interest and a lot to do with Fianna Fáil's interests."