The Courtyard of the British Museum is being redeveloped as a result of the relocation of the British Library. This paper concentrates on aspects of the basement design. In particular attention is focussed on procedures undertaken to ensure the integrity of the Reading Room, which is an important component of London’s architectural heritage. The latter part of the paper refers to the jet grouting and monitoring that has already been undertaken on site (November 1998) and indicates how problems encountered in grouting in the London Clay have been overcome.