Hi Clive,
Ash is not as durable as Iroko, Sapele or Oak, but better than softwood, probably better if furniture is well treated, and dry stored over winter.
I think the export of Teak from Burma, now rebranded as Myanmar, is banned, although Teak is not on the endangered list. The plantation Teak, when available, is probably grown in Indonesia. The last time I saw Teak for sale, on a timber merchants list may be 20 years ago, and it was at least twice the price of Oak then, if memory serves.
Burmese Teak has joined Parana Pine, Brazilian Mahogany, Japanese Oak, Pitch Pine and others, the stuff of legend and old men's stories.
Most Lab benches had Teak tops, including all those miles of them in schools, probably gone up in smoke now, but if anyone happens upon any being removed, stake a claim.