I needed to call the NS&I helpline to get my registered telephone number changed in order to then receive an OTP. The landline number they had for me was in the form +44 01xxxx and I wasn't getting the OTP.
A very helpful sounding voice answered my call and asked for a description of the problem. I couldn't get over the issue of the format of the phone number being the suspected problem and it was only several minutes later as my temper was rising that I realised the "helper" was a bit thick. Usually automated voices are quite readily identifiable. I'm foreseeing problems with this approach.