I am just signing up for the National Savings and Investments online and phone service.
I got a letter this morning with my temporary password, and attempted to login with that password and my premium bonds holder number, but I kept getting the below error:
It turns out that your NS&I number is a different to your premium bonds holder number. You have to wait for this number to arrive by snail mail, sent separately to your password. A careful reading of the password letter does explain this (“you’ll need to wait until your NS&I number arrives in the post”), but I thought I’d mention this in case it catches anyone else.