Health Secretary Patricia Hewitt yesterday insisted no decision had been made on whether to merge West Midlands ambulance services - but revealed a new trust will begin operating on July 1.
The announcement provoked a furious reaction from Conservative MPs.
Birmingham MP Andrew Mitchell (Con Sutton Cold-field) said: "This is a farce. How can she really expect anyone to believe no decision has been made when a new trust will start work in only three months?"
A public consultation on the future of ambulance trusts ended just over a week ago.
The four existing ambulance services in the region - West Midlands, Staffordshire, Coventry and Warwickshire, and Hereford and Worcestershire - could be replaced by one giant service called Central West Ambulance.
The proposal is also strongly opposed by Labour MPs in Staffordshire.
In a House of Commons debate yesterday, Burton MP Janet Dean (Lab) said there was no reason to believe the new service would be as good.
She said: "I do not believe that can be achieved through the amalgamation of Stafford-shire with other services in the West Midlands at this time."
Ms Dean said she would support a merger only when other ambulance services in the West Midlands raised their performance levels and response times to the standards of Staffordshire.
Robert Flello, the Labour MP Stoke-on-Trent South, said other West Midlands forces would drag Stafford-shire down.
"They do not have the system. They do not have the equipment. They do not have the available drugs or protocols available to use them."
Stoke North MP Joan Walley said: "If we go about merging Staffordshire Ambulance Service into a West Midlands Service, we would end up with a far worse service."
Ministers have repeatedly insisted they will listen to the views of local residents, but earlier this month it emerged
Anthony Marsh, currently chief executive of Essex Ambulance Service, had already been appointed to lead the new Central West service.
The Government is also reviewing the structure of primary care trusts and strategic health authorities.
Ms Hewitt said: "No decisions will be taken regarding the reconfiguration of SHAs, PCTs and NHS ambulance trusts before the results of the consultations have been considered and any recommendations reviewed."
Mr Mitchell said: "The ambulance mergers coincide with the creation of a regional police force and fire service. This is part of the Govern-ment's obsession with regional government."