A method of lining an old pipe (1) with a plastics liner (20) avoids the need to excavate a hole at the underground connection (2) between the pipe (1) and a main (3). This is achieved by injecting a flowable sealant material into the annular space between the liner (20) and the pipe (1) such that the sealant extends close to the connection (2). To prevent sealant entering the main (3), the advancing sealant is detected when it approaches the connection (2) by a capacitative sensor (81) located within the liner on a flexible elongate carrier (69). The procedure is carried out with gas in the main (3), a removable plug (67) being housed in a terminator (62) for the liner (20), and the plug being subsequently captured by a connector (68) on the carrier (69) and then withdrawn through the liner. The sensor (81) also enables the liner prior to injection of the sealant to be correctly positioned axially of the pipe (1) according to the type of connection (2).
