Shadow health secretary Andrew Lansley criticised the latest inquiry
The Conservatives say they will order a public inquiry into failings at Stafford Hospital, if they win the next general election.
Shadow Health Secretary Andrew Lansley said the move would allow evidence on many issues to be heard in public.
The former Healthcare Commission said in March 400 people more than expected had died at the hospital and managers had put targets ahead of patient care.
The government has said the problems are already being investigated.
Mr Lansley criticised the latest inquiry, which began last month.
It was ordered by the Department of Health and is being chaired by Robert Francis QC, who has been hearing evidence in private.
Mr Lansley said: "The terms of reference of the current inquiry are frankly insufficient because they do not look at the impact of the tragic events at Stafford."
He said the role of public policy and of central bodies, such as the strategic health authority and the Department of Health, also had to be taken into account.
Relatives of patients who died at the hospital have urged ministers to hold a public inquiry into failings which the watchdog unearthed at the hospital between 2005 and 2008.
The government has rejected such calls.
It previously said the Healthcare Commission investigation had been comprehensive.
In July Health Secretary Andy Burnham announced a second inquiry would be held.
The trust has said lessons have been learned and staffing levels have been increased.