an interesting shape and looks perhaps individually cut not moulded!
However the "static electricity" test works equally with many plastics.
I'd try the "flotation in a saturated salt solution" or small scale scraping test inside the perforation to confirm whether plastic or natural resin, etc.
PS did you ever visit my bead shop at no. 259 near the bridge while you were in Portobello Road? we closed in 2001 after nearly 20 yrs...

Stefany