Policy on regional assemblies is being driven by government 'insiders' at the expense of councils, the New Local Government Network has claimed.
In its report Are we ready for the regions?, NLGN warns that unless councils engage with ministers' devolution plans, assemblies may suck up powers from local government.
It says: 'Overall, the impression is of a regional policy driven by insiders. Some people in local authorities indicated worries that elected regional assemblies may 'suck up' powers from the local level.
'If these same people are not influencing the agenda, then the risk is that this might happen. Their concerns could become a self-fulfilling prophecy.'
Last month's draft regional assemblies bill included a clause that would allow the relevant secretary of state - currently deputy prime minister John Prescott - to award assemblies new powers without recourse to Parliament.
This sparked fears among councils that this provision would lead to powers being sucked up from local government.
Author Warren Hatter, NLGN's head of research, said the majority of interviewees had not been involved in consultations on assemblies, which was reflected in their level of preparations for devolution.
He said: 'A lot of people had the approach that they would deal with it when they had to.
'They did not see it as something that really affected them.'
Mr Hatter said local government risked missing an opportunity to influence how assemblies worked, because it was more used to carrying out instructions from the centre than shaping policy.
'In local government we are so used to being told what to do that it will take quite a while before we are able to confidently drive things forward,' he said.