Britain's most high-powered job share came to an end yesterday when the government agency responsible for combatting the MRSA hospital superbug revealed it has parted company with the two women who headed it since 2001.

Sue Osborn and Susan Williams, joint chief executives of the National Patient Safety Agency, were sent home on indefinite gardening leave in July, pending an inquiry into their managerial record.

Last night the agency said the pair - both aged 54 - have been given early retirement, but it refused to disclose the value of any termination settlement.

Norman Lamb, the Liberal Democrat health spokesman, tabled parliamentary questions to Patricia Hewitt, the health secretary, asking how much taxpayers' money the women were paid during the six-month gardening leave. He said the amount was likely to have been at least £90,000, in addition to the salary paid to Bill Murray, the acting chief executive who took over their work soon after they were sent home. Mr Lamb said there could be no justification for leaving the agency in limbo for so long when it should have been driving forward improvements in the NHS's questionable safety record.

Ms Osborn and Ms Williams were known in Whitehall as "the two Sues". They were paid for 2½ days a week each, but worked for three to create the overlap they thought necessary.

The two Sues had job-shared for 20 years as they worked their way up through five NHS organisations to reach the top of the tree. A few months after taking control at the agency, they told Society Guardian that their strength lay in being able to rely on each other to do the right thing. They came under pressure in July when the Commons public accounts committee said the agency was dysfunctional because it had no idea how many patients died each year as a result of medical error.

The agency is advertising for a new chief executive at a salary of about £130,000.