So, time for the update.
I received the sim, finally, last Friday, having had to wait nearly two weeks from the opening of my account to receive it as the original appeared to have been lost in the post.
It's been in my phone for a week and, frankly, I am unimpressed with the network speeds (average 4Mbs down, slightly more than 10Mbs up) and the fact that the LTE signal appears to keep dropping in and out. In fact, I am so disappointed with the service that I've just cancelled the account under the 14 day cooling off period, which 3 agreed to. Obviously, I appreciate that it's probably down to my location (largish town on the SE coast of the UK) but, from reading the TBB forum thread, I was hoping for so much more.
Ho-hum...