I still wonder why they would need gas cylinders stored on board as most metal work would probably be done in shops, away from the ship, to prevent this very thing from happening.
Speaking to BBC News the Chief Executive of the Cutty Sark Trust, Richard Doughty, said the fire brigade told him they were treating the fire as suspicious.
To limit the amount of decks you have to rip up to get the equipment out to work on it. It could have been something else too. Ship spaces that have been closed up for extended periods of time can build up explosive gases in those spaces. When opened and hitting an ignition source a fir is started. Another one you likely won't believe but is true. Spontaneous combustion due to cleaning gear not properly cleaned before being stowed. I went to many a swab fire the night or two following Field Day on the ship. Wax and stripper is the worse. If you don't get it cleaned out of the mop it will catch on fire in a matter of hours.
Given the materials used at the time, the whole thing is pretty flammable.
AFIK the British Isles no longer have the kind of oak for timbers it would take to build a ship like that. As for the spars, a late clipper like that probably got its spar materials from North America. Large fine-grained softwood timber is pretty well gone too, let alone the curing and drying techniques used at the time. I could be wrong on the latter as an awful lot of work has been done in recent years to recover that knowledge.