The worst fears of district and parish councillors were confirmed today when Secretary of State Hazel Blears gave the go-ahead to create one council to rule the whole of Wiltshire outside Swindon.

It was a bitter pill for the district councils at Kennet and North Wilts to swallow, though the Chippenham-based district council had initially backed County Hall's bid.

Devizes MP Michael Ancram condemned what he saw as a perverse decision. He said: "It is totally against one of the main criteria, that there should be broad cross-section of support from the community.

"All the parish councils I have spoken to, four MPs and four district councils and one opinion poll have all come out against it.

"This is a political act by the Government to undermine the Conservative representation in Wiltshire and I'm sorry that some Conservative members on the county council have fallen into the trap."

County and district councillor Chris Humphries said he was disgusted by the decision, branding it "a disaster".

"Wiltshire is just too large to be administered from one place and it will cost twice as much as it does now," he added.

But County Hall's argument is that the amalgamation of the five councils into one would save £18million a year by 2012, although transition costs are likely to be in the region of £25million.

The new council is expected to be launched in August next year, giving the county council just over a year to get their act together.

Kennet District Council, which has already backed a legal challenge by district councils in other parts of England, is now considering asking for a judicial review of the Government's decision.

Around 300 full-time and part-time jobs at Kennet are under threat from the successful bid, and a similar number at the other three district councils.

Today's statement from County Hall made no reference as to how many positions will be made redundant.

It simply said staff at the district and county councils will get the chance to apply for secondments to join project teams working on the transition.