Job done using the Stanley corded reciprocating saw(as it is called here, rather than sawzall),with Lennox metal cutting blades, and a cutting lubricant. Awkward tight working position in the lazarette and the need to not cut adjacent structures, like the rudder stocks, did not help but we got there. At one stage I tried using a 100mm/4" angle grinder for a short extra cut, too many hot glowing fragments for my liking to continue.
We protected the area with old damp towels, and kept a fire extinguisher handy. The area was vacuumed up immediately after.