Well, it's taken quite a while, ... but my esteemed fifth cousin Denise has finally managed to track down the prodigal Duncan Dunbar Tatham (whom we nicknamed DDT, seeing as he's proven to be almost as much trouble as the insecticide!).
After much diligent searching, Denise has discovered that DDT ("of Ambagamawa") died in 1863, and was buried on the 15th November, 1863, in St Paul's Church, in Kandy, Sri Lanka! More information is, hopefully, on its way - so there might be further news. I'm rapt - can you tell?!
Cheers
Deb