The party, which is closely allied to the Labour Party, said the success of experiments in co-operative service delivery, from small-scale nursing co-ops and community transport schemes to foundation hospitals, was under threat.
It said co-operatives and mutuals could play a major role in voluntary sector public service delivery, but only if they were given more support.
Peter Hunt, general secretary of the Co-operative Party, said: "The Government's position on third sector service delivery looks and sounds great, but no one appears to be learning from the first implementations of this.
"The worst thing that could happen is that we're flavour of the month, new organisations are established and are then left high and dry after only a year."
The party says mutuals, which it defines as non-profit organisations that represent different stakeholders in their management, are particularly suited to public service reform.
The establishment of foundation hospitals was strongly supported by the Co-operative Party as an example of mutualism. But Hunt said that initial government funding to help hospitals become membership organisations had now dried up.
"We've tried to make sure that these organisations succeed," said Hunt.
"But here we are, three years down the line, and the Government has decided to withdraw the support it has given."
The party said the conversion of public bodies into mutuals was also taking place in leisure services and housing. In some areas, local council housing stock is being transferred to member-run community mutual organisations, rather than to housing associations accountable to trustees.
"There will be a requirement for support here as well," said Hunt. "Not only are you converting a public sector organisation into a third sector organisation, but you are going to need additional skills to make the membership structure work."
The Co-operative Party, which is celebrating its 90th anniversary this year, is the fourth largest but least high-profile party in Westminster: 29 Labour MPs are also members of the party, as are eight members of the Scottish Parliament and four members of the Welsh Assembly.