It is not as if we haven't had this or a similar problem before when VM had to do a lot of work to ensure that Outlook's servers could communicate properly with those of VM. That was a couple of months ago and the issue went away.
It would be helpful to know from the OP what Outlook interface he is seeing. Microsoft are in the process of upgrading Outlook.com to a new web based interface for all their domains - like Hotmail - with new protocols.
The way to tell is to look at the banner on top of the display. If it says "Outlook Email" it is the new interface. If it says Outlook.com it is the old interface. So tell us please.
The next thing I want to know is whether the ntlworld address is still live. If VM addresses are not DIRECTLY accessed for 90 days they are suspended and deleted after 60 days. So would the OP please tell us whether the address is working properly in VM web mail?
Once we have this we'll be able to advise further. I suspect VM will need to look at this one anyway. There could be a simple fault in the OP's VM mail box.
Superuser 2017/18 Use Kudos to say thanks Mark answer as "helpful" only when the problem is solved Please don't send me private messages unless I ask you to. I do not work for VM. The advice I give is based on my best understanding of VM policy and practice. You rely on it at your own risk.