Not myself, but it appears that you have to get a GWR to Plymouth and then a XC to Edinburgh. Dunno about GWR but XC have room for 3x bikes on a regular train, they are hung up by the fron t wheel. 2x bike areas, one holds one bike and the other holds 2.
May be a push with a full touring setup.
Penzance to Edinburgh? Anyone have first hand experience? Loaded touring rig.