The merger of the Midlands ambulance services has been thrown into further disarray amid confusion over a two-year deadline for the best-performing trust to join.
Last week the Government announced that four of the services - the West Midlands, Coventry and Warwickshire, Shropshire, and Hereford and Worcester - would amalgamate from July 1.
Staffordshire, which has the best response times in the country, was told it could remain independent but only "for up to two years".
Notes attached to a letter sent to MPs by David Nicholson, acting chief executive of the new West Midlands Strategic Health Authority (SHA), said the trust would merge with the other services in July 2008.
However, Burton MP Janet Dean said she had received personal assurances from Lord Warner of Brockley, Minister of State for Reform based in the Department of Health, and Health Minister Andy Burham that no such timetable was planned.
"Somehow the two-year reference remained in some parts of the correspondence but I have been assured that Staffordshire Ambulance Service will remain independent for the foreseeable future," she said.
"There is no timetable for any amalgamation but we are working towards joining the other ambulance trusts at some point.
"I've had it direct from the Minister's office and Lord Warner that there is no intention to merge Staffordshire Ambulance Service on any timetable at any time."
Lichfield Tory MP Michael Fabricant, who has been part of a cross-party group campaigning against the merger of the Staffordshire service, said he had formally tabled questions for Health Secretary Patricia Hewitt to clarify the situation.
Mr Fabricant said "assurances" were "meaningless and can easily be reversed". "This whole issue has become a shambles," he said.
"At the beginning of the week the Government was clear: merger within 24 months. Have they now changed their minds or what? Nothing is clear or in writing.
"The ministerial replies are public, official and are published in Hansard for all to see. I expect to receive replies within the next week or so. Only then, and not before, will we know if Staffordshire Ambulance Service has been saved."
Staffs ambulance bosses feared its high levels of performance would be compromised if it amalgamates with the other trusts to form the new West Central ambulance service, which will serve more than four million people.
Roger Thayne, who stepped down as chief executive of Staffordshire Ambulance Service in March after claiming it was already a "done deal", said he was still opposed to the merger.
He now runs Wales Ambulance Service, which under-went a similar exercise in 1998 and, he said, as a result its performance levels saw it slip from being one of the best in Britain to one of the costliest and poorest performing trusts.
"There's a warning for us in that," he said. "Someone must realise this is not the way forward - big isn't necessarily beautiful.
"WAS has ended up being the most expensive ambulance service in Britain, and one of the poorest in terms of response times
"Taken as a whole, the trusts which cover the West Midlands have the best service record in the country, but they can't maintain that level as one merged trust.
"The public were very much against the merger, as am I.
"I think Janet Dean is wrong, and unless the Government publicly states Staffordshire Ambulance Service will never be merged, I don't think we can assume the service is safe."