a method of lining tubing within a wellbore comprises applying a polymerisable fluid composition containing a photoinitiator to the interior surface of that tubing and initiating polymerisation of the composition by exposing it to actinic radiation , suitably light or ultraviolet with wavelength 250 to 800 nm . the composition is preferably stable against heat but polymerises quickly when exposed to the actinic radiation . the composition may be spread onto the tubing and exposed to actinic radiation as soon as it has been spread into a layer , suitably with a tool which skims the tubing surface with applicator pads for dispensing and spreading the composition , immediately followed by exposing the spread composition to actinic radiation . a second option is that the composition is provided as a sleeve which is expanded against the tubing , exposure to actinic radiation preferably then being achieved using light guides or light emitting diodes within the sleeve .