The document includes a statement by health secretary Alan Johnson in which he says Labour has "got it wrong" over the sharing of wards. The government has repeatedly said that it plans to change the practice.
Mr Johnson is quoted as saying: "Sane and rational arguments about why it can't be done no longer cut it with me, it's going to happen."
Prepared by a senior NHS manager, the memo suggests ministers are getting ready to act.
The manager wrote: ‘There is no doubt that the Tories have rattled Labour over the failure to meet promise of ending mixed-sex accommodation.
‘Expect a revised definition that simply makes it clear that men and women and children and adults will no longer share the same accommodation. Everything is included in that definition, except accident and emergency.’
Recent data from the Conservatives showed roughly one in seven of hospital trusts still used at least one open-plan mixed-sex ward while in some areas curtains were still being used to segregate patients.