The construction of the Jubilee line Extension Station at Westminster, London was predicted to produce significant movements of the Big Ben Clock tower and the adjoining Palace of Westminster. The works consisted of the excavation of two vertically stacked 7.4 m tunnels and a 39 m deep station escalator box respectively located 28 m and 34 m north of the foundations of the Clock Tower. The protective measures adopted to minimise damage to these priceless historic buildings consisted primarily of compensation grouting below the Clock Tower and proved extremely effective in controlling settlement and tilt of the structure. This case study not only demonstrates the success of this protective measure, but also shows the value of careful interpretation of appropriate numerical modelling and the results of high quality monitoring during and after completion of the works.