Studies of legislatures focus on what happens in formal space, principally the chamber and committee rooms. Such studies are necessary, but not sufficient, for explaining behaviour within legislatures and its consequences. The use of space for member to interact informally with one another – informal space – can contribute to the institutionalisation of a legislature through facilitating autonomy. Such space provides an arena for socialisation, information exchange, lobbying, and mobilising political support. This paper examines the significance of informal space, drawing on the experience of the UK Parliament.