Forcing warring practices to create large CCGs "may not be the best thing for patients".
It is claimed CCG mergers should not be imposed for fear of trust issues emerging.
Speaking at the NHS Alliance's annual conference in Manchester yesterday (30 November), Dame Barbara Hakin, National Manager of Commissioning Development at the Department of Health, said small CCGs may be forming "due to poor relations with neighbouring practices".
She warned "it may not be the best thing for their patients" if we force such practices to come together.
Birmingham's Healthworks Commissioning Consortium has merged with a number of CCGs to bring its patient population up from 150,000 to 400,000.
The consortium's Lead GP, Dr Nick Harding, attributes its success with the fact practices were given the freedom of choice.
"It is easier to trust that a bigger CCG will work if you have taken the decision to merge, rather than it being forced upon you," he said.