Today I started with removing the RH boot door.  This once again required the screws to have their heads drilled off.  Having removed the door, I was able to remove panelwork along the top of the boot opening and down the RH side.  This revealed extensive wet fungal rot in the base of the two pillars at the RH side of the boot opening and this will need to be repaired by jointing new lower sections of timber.

Right-hand boot door frame timbers

RH corner of boot door frame

I started the job of replacing the rotted timber by cutting both the pillars just below the corner horizontal (with the hole) visible in the picture.  I cut a step into the good wood in order to make a strong joint with the new timber.