Riccati-type control for a class of nominally linear large-scale systems composed of identical subsystems and symmetric interconnections is presented. Symmetric composite systems with bounded uncertainties in parameters both in subsystems and interconnections system matrices are considered for decentralised output control design using a controller-observer scheme. The controller-observer is designed for an auxiliary artificial uncertain system whose dimension is equal to the dimension of a subsystem in the original system. Conditions for the validity of this procedure are proved and illustrated on a numerical example. Matching conditions are not needed.