Subsequent to this post the e-mail did come through - so I was able to proceed. I think there should be something on their support site about this though as this was my third attempt to join. I have tried repeatedly to register with User Testing to no avail. It gets to the page telling me they have sent an e-mail to me and I must confirm by checking that e-mail and nothing comes through to my e-mail inbox. I suspect it might be an issue because of the country in which I reside? Whatever the issue, the FAQ on the "support centre" site do not help.