Took the extruder off the carriage tonight to have a look at how bad the damage was. To be honest I was hoping that it’d be a simple matter of screwing the brass back into the PTFE but no such luck.
As you can see the actual body of the extruder has deformed and cracked. I wouldn’t have thought that the PLA would buckle this easily but I guess that the heat from the hot end will have risen and softened the plastic a bit. Anyway looks like a new body will have to be sorted before repairs can proceed. To prevent this happening in the future the only thing I can think of would be to decrease the limit on the extrusion speed to reduce the pressure in the hot end.