Liquid air energy storage (LAES) is a technology for bulk electricity storage in the form of liquid air with power output potentially above 10 MW and storage capacity of 100 s MWh. In this paper, we address the performance of LAES and the experimental evidences gathered through the first LAES pilot plant in the world developed by Highview power storage at Slough (London) and currently installed at the University of Birmingham (UK). We developed a numerical model of LAES plant and carried out an experimental campaign to gather new results which show the LAES operating principles, the reliability of the technology, the startup/shut down performance, and the influence of operational parameters. In summary, this work (a) contributes to the advancement of thermomechanical storage systems, (b) provides new experimental evidences and results for LAES technology, and (c) highlights the crucial aspects to necessarily improve the performance of LAES.