In this paper a design approach for a sensorless controlled, brushless, interior permanent magnet machine is attained. An initial study based on established electrical machine formulas provides the machine's basic geometrical sizing. The next design stage combines a particle swarm optimisation (PSO) search routine with a magneto-static finite element (FE) solver to provide a more in depth optimisation. The optimisation system has been formulated to derive alternative machine design variants, subject to the design constraints, in a computationally efficient manner using as few FE simulations as required. Moreover a parallel computing approach has been used for the most computationally intensive processes. The optimisation system objective function aims to find a solution satisfying all the machine's design requirements including the torque-speed envelope and compatibility with the high-frequency injection based sensorless operation, whilst minimising the machine weight. A holistic approach is presented where a complete machine, including the stator and rotor sub-assemblies are designed accounting for all the required performance measures under the high-frequency injection based sensorless operation. The efficacy of the new approach has been demonstrated on a design case study with consecutive design stages discussed in detail. Also, the paper provides conceptual information regarding practical implementation of the proposed optimisation system together with an insight into the definition of the objective function and its influence on the design solutions. Furthermore, the calculated results from the optimisation system have been compared with direct FE predictions for the design exemplar showing good correlation.