Local government minister John Healey confirmed five successful unitary proposals last week in Wiltshire, Cornwall, Durham, Northumberland and Shropshire. Bedford's proposal is still being considered.
The five unitary bodies are expected to be in place by April 2009 and could save a combined total of more than £75 million each year, the DCLG maintained.
Five separate authorities will combine to create the Wiltshire unitary council. Kennet District Council head of forward planning Ed White said the effects on planning services in both the short and long terms are a major concern.
He told Planning: "District councils are leaking planning staff who are worried about the future of their jobs. This raises questions as to how soon the new authority will be able to replace them."
Staff are moving to existing unitary authority Bath and North East Somerset Council or being poached by private sector consultancies, White said. He added that North Wiltshire District Council will soon be left with "0.6 of a planner" in the forward planning team.
North Wiltshire head of policy and performance Lachlan Robertson said: "We will shortly experience considerable staff shortages in planning and these can to some extent be attributed to the unitary decision."
The move will slow down delivery on the local development framework (LDF). The council is urging an early merger of all Wiltshire LDFs, Robertson said.
Since July, nine staff from development control and two in planning policy and conservation have left or are planning to leave West Wiltshire District Council.
A joint judicial review into Shrewsbury and Atcham and Congleton Borough Councils' cases against unitary authorities in their counties will be heard in January after they went to the Court of Appeal.
Ministers are already rethinking plans for two unitaries in Cheshire after major opposition. Proposals for Exeter and Ipswich will also be reassessed after failing affordability criteria.