Cheers to all. Turns out that Plantronics were doing some site
maintenance and had taken it down deliberately.

To keep it on topic, I purchased a bluetooth headset from myself which
failed to work. It had been in stock for some time and I think the
battery had just siezed as there was no sign of life at all.

I did not have any left in stock to exchange with, so I used the
plantronics warranty service, and without any fuss at all I now have an
upgraded model on the way to me free of charge.

Excellent service plantronics, well done.