A decentralised control design methodology, which is based on ideas from robust stabilisation using the normalised left coprime factorisation and the gap metric, is developed. Some indicators for decentralised control design are proposed. These indicators are useful as a guideline for screening alternative control structures. A sufficient stability condition is formulated by making use of these indicators. Unlike the Relative Gain Array (RGA), these indicators can guarantee the stability and achievable performance of the system under decentralised control for given design specifications. This methodology has been applied to two industrial case studies in which the systems are open-loop unstable and/or non-minimum phase.