A disability charity has said it has "some worries" about plans to merge services at three of London's councils.
Hammersmith and Fulham, Kensington and Chelsea, and Westminster have proposed combining areas such as social care, education, libraries and property management to save up to £35m a year.
The Westminster Society for People with Learning Disabilities said decision making would become "far more complex".
And a Labour councillor questioned the accountability of joint departments.
A 100-page document drawn up by the three Conservative-run boroughs proposed halving the 350 middle and senior managers by 2014/15.
It also suggested a 54% budget cut in adult social care, which employs more than 260 people.
'Not made clear'
But Gabby Machell, the chief executive of the disability charity, said: "I'm not sure that such a large directorate, overseeing three sets of individual services and needs, will actually understand the needs of each borough.
"We've been in existence for 50 years. We understand the needs of this part of the borough of Westminster in a way that no other organisations will understand.
"We would have some worries about how we get from this position to that position."
Barrie Taylor, a Labour councillor in Westminster, claimed the new arrangement "certainly won't be publicly accountable".
"You've got no idea where you're going to be able to take your queries. You won't be able to know how to complain.
"Suddenly the accountability issue about local politicians is taken somewhere else.
"Where is it? Where do we take that debate? Into each of the three councils? Or into a super-borough meeting?
"Nobody has made that clear at all."
But the three boroughs were "absolutely committed, and we have specifically guaranteed, that we will not lose our connection with local people", said Colin Barrow, the leader of Westminster Council.
"We are not creating one council. We are three sovereign boroughs, agreeing to work together to pool some of our services.
"Residents shouldn't notice the difference."
Each council's cabinet is to discuss the plans over the next fortnight.
Eight Labour-run boroughs across London are also considering whether to merge services.