That was my thoughts, Danny, but apparently the main feed for the electricity and water go up there, so it'd need to be done very carefully!!
At the end of the day, the only solution is to provide a much easier way for the water to get out - land drains against the wall, put in with a mini digger, with the end of the drain coming out in the drain pit at the near end of the barn. Removing the spoil to sufficient depth is a slightly dodgy solution as the next barn's only about 8' away and if we cause subsidence in that I suspect there will be proper upset! If we just dig the spoil away from the barn, it'll slump back down pretty quickly, as it's clay.
PVA is definitely NOT the solution here!