Unions have complained that they were not consulted adequately and a local Conservative MP, Ian Liddell-Grainger, has accused the partnership’s member of excessive secrecy over its formation.
The commission’s report has found that Somerset and Taunton Deane’s “procurement and governance arrangements were robust”.
It agreed that projected£200m savings over 10 years were achievable.
Somerset’s portfolio holder for resources and finance Dave Green (Lib Dem) said: “This report should give everyone in Somerset confidence in what [the councils] have done and are achieving through Southwest One.”
Southwest One will handle information technology, human resources, finance, property and facilities management, revenues and benefits, procurement and customer call centres for its members.
Other public bodies in the region have been invited to join.