The service they will give you i.e outline proposal is worth 1% of the total estimated cost
http://www.a4architect.c...bout-us/fees-breakdown/ Its therefore a psychological assumption that the design is cheaper using them since if you approach any independent architect and demand for the same level of service, they will give it to you at the same price or even cheaper.
The same council guys will still look for the independent registered architect for his signature which they pay so with the independent architect, he can offer the service at this outline proposal level at a lesser cost since he does not need to pay any other third party for signatures.
Assuming a house costs 2m to construct, 1% of this is 20k.The council guy will charge you this plus another say 10 k on top for the architect's signature while the architect will charge you only the 20k for the same level of service.
As Iron Sharpens Iron, So one Man Sharpens Another.