A method of forming a tubular conduit in a borehole, wherein the borehole is closed by means of a pressure barrier capable of sustaining a borehole pressure and having at least one pressure sealable inlet, comprises: introducing a substantially flat, elongate flexible member into the borehole; and forming the flexible member into a tubular form to define the conduit inside the borehole below the pressure barrier. An apparatus for forming a tubular conduit in a borehole closed by a pressure barrier capable of sustaining a borehole pressure and having at least one pressure sealable inlet, comprises: a supply of a substantially flat, elongate flexible member; a feed system for introducing the member into the borehole; and a former below the pressure barrier for forming the flat member into a substantially tubular conduit in the borehole.