Thanks very much for the advice - and I can certainly ignore the problem now that I am 'in the know'.
If Now TV are struggling to fix this bug though they could maybe add a little bit to their emails to inform customers that if the link takes them to that page they are good to go - wouldn't be half so stressful for us delicate little technophobes :-)
I don't think it's a bug, it's just them being insidious and trying to get more money out of new custormers that panic and buy a voucher. It's a marketing ploy, they know very well what they're doing and there's no reason to get rid of it. At least not from their perspective.
Would anyone else be able to confirm that I can safely ignore that "complete your account" message or do I need to go into the live chat for my broadband to go live?